Different logo for mobile – 2020 CSS

and you really want to change the logo only for mobile devices – or do you mean for small screen widths?

for mobile devices put this to your child-theme functions.php

add_filter('avf_logo','av_change_mobile_logo');
function av_change_mobile_logo($logo){
    if(wp_is_mobile()){
      $logo = "/wp-content/uploads/mobile-logo.png";
    }
    return $logo;
}

and if you want to have on mobile devices a different transparency logo:

function av_change_mobile_transparency_logo($header){
    if(wp_is_mobile()){
        $header['header_replacement_logo'] = "/wp-content/uploads/mobile-transparent-logo.png";
    }
    return $header; 
}
add_filter('avf_header_setting_filter','av_change_mobile_transparency_logo');