Changing fonts does not work

First of all – your business location is Germany – so you had to be GDPR (DSGVO) compliant.
For that reason – do you have any entrance inside your theme to hamper google font support of the theme. F.e. via a snippet plugin?
like:

function my_output_google_webfonts_script( $activate ){
  return false;
}
add_filter( 'avf_output_google_webfonts_script', 'my_output_google_webfonts_script', 10, 1 );

OR

function enfold_customization_switch_fonts() {
    global $avia;
    $avia->style->print_extra_output = false;
}
add_action( 'init', 'enfold_customization_switch_fonts' );

you only uploaded open-sans and din-alternate-cdnfonts

Next question: on your video i see that you are using a child-theme – but on your live site i do not see that you are using it?

ON your Privacy setting : if i accept using Google Web fonts i see:

my recommendation on GDPR compliance : use selfhosted fonts – upload them via font-manager as you did with open-sans.
Then you do not need to mention the google webfont usage hint on privacy.

i see this in your DOM:

no child just enfold.

next: see if i switch on the usage of google web fonts via your privacy settings:
https://webers-testseite.de/jeroch.mp4

on your @font-face rules a lot of open-sans and one Din font:

activation of uploaded Fonts : the list of uploaded fonts is at the end of that enfold list:

something went wrong with your uploading ( on that child-theme with din-pro-light ) –
and yes i have seen that on your video the child was activate ( but now the theme itself is in use)