Fullwidth Easy Slider: takes too long to load – images are too hgh

can you make the link public? i can not believe that a 200kb image loads that way.
it it is your photopage – use please original dimensions and not the 1500x1000px croped images.

One Problem is that the original images are often better compressed than the cropped images of enfold. Because they do not compress those files.
so from your image: 0411_D1A_5462.jpg (205kb) on original upload it becomes a cropped image 0411_D1A_5462-1500×1000.jpg with 884kb.

So use for those big images alway your optimized originals.
Or use those mentioned tools of ismael.

a 3:2 aspect ration could hardly forced to show on a 16:9 Screen. If you can live with black borders you can choose not to cover but to contain the image – means the full image is shown centered and it depends on image orientation and dimension where those borders are.

ja und nimm die Original Bilder: Slideshow Image and Video Size : no scaling

wenn du möchtest, dass die Bilder oben unten nicht über den Screen gehen. kann man das erzwingen:
gib der full-width slideshow eine Custom Class. ich habe das mal mit zweien deiner Bilder gemacht, und der Slideshow die klasse: vollehoehe
gegeben.

dann habe ich ins quick css folgendes eingegeben:

.vollehoehe img {
    max-height: calc(100vh - 170px);
}

die minus 170px sind dem Header-bereich geschuldet. Da kannst du noch ein wenig dran drehen.
https://webers-testseite.de/slide-show/

wenn du es gesehen hast – nehme ich die Bilder wieder raus.

Wenn du es nur auf der startseite hast kannst du es auch so selectieren:

.home .avia-slideshow img {
    max-height: calc(100vh - 170px);
}

i can not confirm to that – your page loads on my end fast enough.
but i have a 200mbit connection

but see here your results: https://gtmetrix.com/reports/fotowalther.ch/L1YaUTiT

it seems that you have no gzip compression enabled ! (this is relevant for performance)
and no leverage browser caching is defined and no expires header is set.

i do always activate it via the htaccess file ( but it depends on your server) but commonly they serve as an apache server.
this is a hidden file ( .htaccess) – but a lot of ftp clients can make them visible on default.
you can download the file ( if you have f.e. a different permalink set – there will be one) via ftp – rename it to htaccess.txt and edit it with a good text editor ( f.e. : sublime text for mac or notepad++ for Windows)

on default there will be something like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

this existing entries have to be be untouched and depends on your settings you made in the dashboard.
Most of the caching tools put in a lot of entries here.

My settings for example are in front of that existing entries: ( means in front of # BEGIN WordPress):

# Secure your wp-config
# Disallow access to important files
<FilesMatch "(^\.|wp-config\.php|xmlrpc\.php|(?<!robots)\.txt|(liesmich|readme)\.*)">
   Require all denied
</FilesMatch>

# secure htaccess-file
<files ~ "^.*\.([Hh][Tt][Aa])">
order allow,deny
deny from all
satisfy all
</files>

# Keep-Alive
<ifModule mod_headers.c>
   Header set Connection keep-alive
</ifModule>
 

# Gzip
<IfModule mod_mime.c>
    AddType application/javascript          js
    AddType application/vnd.ms-fontobject   eot
    AddType application/x-font-ttf          ttf ttc
    AddType font/opentype                   otf
    AddType application/x-font-woff         woff
    AddType application/x-woff              woff
    AddType image/svg+xml                   svg svgz 
    AddEncoding gzip                        svgz
</Ifmodule>
 

# GZip Kompression
<IfModule mod_gzip.c>
 mod_gzip_on       Yes
 mod_gzip_dechunk  Yes
 mod_gzip_item_include file      \.(html?|txt|css|js|svg|php|pl)$
 mod_gzip_item_include handler   ^cgi-script$
 mod_gzip_item_include mime      ^text/.*
 mod_gzip_item_include mime      ^application/x-javascript.*
 mod_gzip_item_exclude mime      ^image/.*
 mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.*
</IfModule>

 
# Browsercache
<IfModule mod_expires.c>
 ExpiresActive On
 ExpiresDefault "access plus 1 month"
 ExpiresByType text/css "access plus 1 month"
 ExpiresByType text/javascript "access plus 1 month"
 ExpiresByType text/html "access plus 1 month"
 ExpiresByType application/javascript "access plus 1 month"
 ExpiresByType application/x-javascript "access plus 1 month"
 ExpiresByType application/x-font-ttf "access plus 1 month"
 ExpiresByType application/x-font-woff "access plus 1 month"
 ExpiresByType application/x-woff "access plus 1 month"
 ExpiresByType application/xhtml-xml "access plus 600 seconds"
 ExpiresByType application/pdf "access 1 month"
 ExpiresByType image/gif "access plus 1 month"
 ExpiresByType image/jpg "access plus 1 month"
 ExpiresByType image/jpeg "access plus 1 month"
 ExpiresByType image/svg+xml "access plus 1 year"
 ExpiresByType image/svg "access plus 1 year“
 ExpiresByType image/png "access plus 1 month"
 ExpiresByType image/x-icon "access plus 1 month"
</IfModule>

 
# Deflate by FileType
<IfModule mod_deflate.c>
 AddOutputFilterByType DEFLATE text/plain
 AddOutputFilterByType DEFLATE text/html
 AddOutputFilterByType DEFLATE text/xml
 AddOutputFilterByType DEFLATE text/css
 AddOutputFilterByType DEFLATE text/javascript
 AddOutputFilterByType DEFLATE image/svg+xml
 AddOutputFilterByType DEFLATE application/javascript
 AddOutputFilterByType DEFLATE application/xml
 AddOutputFilterByType DEFLATE application/xhtml+xml
 AddOutputFilterByType DEFLATE application/rss+xml
 AddOutputFilterByType DEFLATE application/atom_xml
 AddOutputFilterByType DEFLATE application/x-woff
 AddOutputFilterByType DEFLATE application/x-font-ttf
 AddOutputFilterByType DEFLATE application/x-font-woff
 AddOutputFilterByType DEFLATE application/javascript
 AddOutputFilterByType DEFLATE application/x-javascript
 AddOutputFilterByType DEFLATE application/x-shockwave-flash
</IfModule>
 
# ETag
Header unset ETag
FileETag None

you see here both the older gzip and the more modern mod_deflate module.
on mod_expires you can set different time settings – optimized for your website.

After uploading this htaccess.txt file – rename the existing .htaccess to htaccess.bak ( to have a fallback)
then rename the new file to .htaccess(be carefull to set the dot before the file) – maybe it is a good advice to set the file permissions to 640.

did you set the Enfold options to load only used element
and try to deactivate jQuery-migrate! If you have no films on your page deactivate these setting too (youtube and selfhosted videos) etc.

Allways empty all cachings. and on Performance checkmark: Delete old CSS and JS files?

check if your hoster limits your PHP-Memory Limit usage to the installation.
You can ( if they allow those settings) enlarge it via wp-config.php entries:
place it f.e. just behind: define('WP_DEBUG', false);

define( 'WP_MEMORY_LIMIT', '256M' );

check what your hosting supports for you