or even better – just use the team-member element as it is and parse a popup by your own.
see with snippet on that example page: https://webers-testseite.de/teammember-vitae-2/
PS: It is always best to examine each individual case closely, as this is the only way to offer a customized solution. Otherwise, one indulges in speculation.

The last solution has the advantage that you only use the pure Enfold element for team members and then create your own lightbox with it. Disadvantage: you would have to rebuild your page and discard our previous design. In the window on the right side of the page, you can see that only plain text is entered in the Description Input Fiele — the Lightbox retrieves the image, name, and position from the existing DOM elements.
To change the aria-label – just edit these lines:

tPrev: 'Previous Biography',
tNext: 'Next Biography',

i remember we made for your “leadership” members an own popup script f.e.
if you only want to change that aria-labels of that popup script – then the solutions above are not neccessary. Only change that inline popup script
so try to replace that script inside the functions.php snippet by (remove temporarly the observer script above)

window.addEventListener("DOMContentLoaded", function () {	
	(function($) {
		$('#people').each(function(){
		var that = this;
			$('.flex_column', this).each(function(i){
				if($(this).find('.mfp-hide').length){
					$(this).find('.bio-link').attr('href','#bio-'+(i+1)).addClass('no-scroll');
					$(this).find('.avia_image').attr('href','#bio-'+(i+1)).addClass('no-scroll');
					$(this).find('.mfp-hide').attr('id','bio-'+(i+1)).addClass('white-popup');
				}
			});
		});

		$('#people .flex_column').find('a[href^="#bio-"]').magnificPopup({
			type:'inline',
			midClick: true,
			removalDelay: 500,
			mainClass: 'avia-popup mfp-fade people',
			gallery: { 
				enabled:true,
				arrowMarkup: '<button title="%title%" type="button" class="mfp-arrow mfp-arrow-%dir%" aria-label="%title%"></button>',
				tPrev: 'Previous Biography',
				tNext: 'Next Biography',
			},
		});

		$('#people .flex_column').find('.avia_image[href^="#bio-"]').magnificPopup({
			type:'inline',
			midClick: true,
			removalDelay: 500,
			mainClass: 'avia-popup mfp-fade people',
			gallery: { 
				enabled:true,
				arrowMarkup: '<button title="%title%" type="button" class="mfp-arrow mfp-arrow-%dir%" aria-label="%title%"></button>',
				tPrev: 'Previous Biography',
				tNext: 'Next Biography',
			},
		});

	})(jQuery);
}); 

better see next solution
PS you can get rid of style part – and place the css inside quick css.

It depends a little on how you want to use it. If you only want to change this to “next bio” and “previous bio” for certain custom classes, we would need to rewrite this code a little.

f.e. if you have a gallery – then you can give a custom class to that gallery element (f.e. team-member)

function add_magnific_popup_aria_labels() {
    ?>
    <script type="text/javascript">
    (function($) {
        'use strict';
        
        if (typeof $.avia_utilities !== 'undefined' && typeof $.avia_utilities.av_popup !== 'undefined') {
            
            var originalOpenCallback = $.avia_utilities.av_popup.callbacks.open;
            
            $.avia_utilities.av_popup.callbacks.open = function() {
                
                if (typeof originalOpenCallback === 'function') {
                    originalOpenCallback.call(this);
                }
                
                var self = this;
                
                setTimeout(function() {
                    // Determine labels based on the gallery container
                    var prevLabel = 'Previous image';
                    var nextLabel = 'Next image';
                    var closeLabel = 'Close lightbox';
                    
                    // Check if the clicked element (currItem.el) is inside a container with a custom class
                    if (self.currItem && self.currItem.el) {
                        var $link = $(self.currItem.el);
                        
                        // Find the parent lightbox container element
                        var $lightboxContainer = $link.closest('.avia-gallery, .av-masonry, .av-horizontal-gallery');
                        
                        if ($lightboxContainer.hasClass('team-member')) {
                            prevLabel = 'Previous person';
                            nextLabel = 'Next person';
                            closeLabel = 'Close biography';
                        } else if ($lightboxContainer.hasClass('products-gallery')) {
                            prevLabel = 'Previous product';
                            nextLabel = 'Next product';
                            closeLabel = 'Close product gallery';
                        } else if ($lightboxContainer.hasClass('projects-gallery')) {
                            prevLabel = 'Previous project';
                            nextLabel = 'Next project';
                            closeLabel = 'Close project gallery';
                        }
                        // Add more conditions as needed
                    }
                    
                    $('.mfp-arrow-left').attr('aria-label', prevLabel);
                    $('.mfp-arrow-right').attr('aria-label', nextLabel);
                    $('.mfp-close').attr('aria-label', closeLabel);
                }, 50);
            };
            
            var originalChangeCallback = $.avia_utilities.av_popup.callbacks.change;
            
            $.avia_utilities.av_popup.callbacks.change = function() {
                
                if (typeof originalChangeCallback === 'function') {
                    originalChangeCallback.call(this);
                }
                
                var self = this;
                
                // Update labels when changing images
                var prevLabel = 'Previous image';
                var nextLabel = 'Next image';
                
                if (self.currItem && self.currItem.el) {
                    var $link = $(self.currItem.el);
                    var $lightboxContainer = $link.closest('.avia-gallery, .av-masonry, .isotope, .av-horizontal-gallery');
                    
                    if ($lightboxContainer.hasClass('team-member')) {
                        prevLabel = 'Previous person';
                        nextLabel = 'Next person';
                    } else if ($lightboxContainer.hasClass('products-gallery')) {
                        prevLabel = 'Previous product';
                        nextLabel = 'Next product';
                    } else if ($lightboxContainer.hasClass('projects-gallery')) {
                        prevLabel = 'Previous project';
                        nextLabel = 'Next project';
                    }
                }
                
                $('.mfp-arrow-left').attr('aria-label', prevLabel);
                $('.mfp-arrow-right').attr('aria-label', nextLabel);
            };
        }
        
    })(jQuery);
    </script>
    <?php
}
add_action('wp_footer', 'add_magnific_popup_aria_labels', 999);

you see this line includes masonry etc. if you like:

// Find the parent lightbox container element
var $lightboxContainer = $link.closest('.avia-gallery, .av-masonry, .av-horizontal-gallery');

I remember the team members very well. Didn’t we write an extra pop-up script for that? Maybe it would be better to add a call-back there.
You could also try hooking into the magnificPopup script and using the callback function to insert the aria labels.

function add_magnific_popup_aria_labels() {
?>
<script type="text/javascript">
(function($) {
'use strict';
        
        // Extend the existing MagnificPopup callbacks
        if (typeof $.avia_utilities !== 'undefined' && typeof $.avia_utilities.av_popup !== 'undefined') {
            
            // Save the original open callback function
            var originalOpenCallback = $.avia_utilities.av_popup.callbacks.open;
            
            // Overwrite the open callback function
            $.avia_utilities.av_popup.callbacks.open = function() {
                
                // Execute the original function
                if (typeof originalOpenCallback === 'function') {
                    originalOpenCallback.call(this);
                }
                
                // Add aria-labels to the navigation arrows
                setTimeout(function() {
                    $('.mfp-arrow-left').attr('aria-label', 'Previous Bio');
                    $('.mfp-arrow-right').attr('aria-label', 'Next Bio');
                    $('.mfp-close').attr('aria-label', 'Close Lightbox');
                }, 50);
            };
            
			// Also add a change callback to ensure 
			// that the labels are still present when the images change.
            var originalChangeCallback = $.avia_utilities.av_popup.callbacks.change;
            
            $.avia_utilities.av_popup.callbacks.change = function() {
                
                // Execute the original function
                if (typeof originalChangeCallback === 'function') {
                    originalChangeCallback.call(this);
                }
                
                // Ensure that aria-labels are present
                $('.mfp-arrow-left').attr('aria-label', 'Previous Bio');
                $('.mfp-arrow-right').attr('aria-label', 'Next Bio');
            };
        }
})(jQuery);
</script>
<?php
}
add_action('wp_footer', 'add_magnific_popup_aria_labels', 999);

PS – if you only want to avoid that on small screens the slider images will be less height then the inner content. there will be an option to have a min-height for it:

the fullwidth slider is a responsive slider. That means – the images are set to 100% width and height depends on aspekt ratio of your image.
so if you like to get a fullwidth slider to be 50% height of the image – then your images must have an aspekt ratio of 2:1

if you force the slider to have 50vh height …. then you will have on smaller screens a space between the slider and the next section:

or to force that behaviour – you will then have a distortion of the images – see:
https://webers-testseite.de/fullwidth-slider/
and pull the browser-window bigger and smaller

________

this is a fullscreen slider forced to be that way – but then images are cropped.
https://webers-testseite.de/full-screen-slider/