I have some advice what you could do if Google does not accept your assigned meta description.
Firstly, you can check your competitors' meta descriptions and try to write your own description so that it hits the same tone. So, for example, if your competitors mention their own brand or use a specific term, you should try that too. Or if all your competitors in front of you do NOT use a call-to-action, you can try without one to avoid being too much of a "salesman". The key is to capture the “DNA” of the ideal meta description based on what is already successful on Google.

But if you've already done everything, check your website's source code and make sure that the text you want is actually in the HTML <meta name="description" content="" /> field. If you only rely on browser extensions, you may receive incorrect information here (browser extensions can also make mistakes). The source code always provides a definitive answer here. If that doesn't bring any improvement, you still have the option of analyzing which passage of text on your page is used by Google to generate the meta description. You could try changing this text on your page to prompt Google to re-consider it. This could result in Google now following your meta description suggestions, although there is no guarantee.

Source:
https://seo-monkey.de/ratgeber/was-ist-seo/#metatitel-optimieren

Yes as mentioned google have own criteria for that. Use google search console and debug your website.

but I found the issue

the META - Title has to be at least 40 characters and the description at least 121 characters for google to accept it

and why does every website has a nice description then?

that is what a "META Description is for" - google search result description

like described here

https://wordpressforgood.com/how-to-edit-page-title-and-description-in-google-search-results-2/

Meta is placed fine in your code, showing it on google its entirely depends on the google. You can not control what they show in search content.

this field is not even working

my description:

-
-
what google says

-
-

I changed it few days ago

Yes but don't add it otherwise all pages will have same description.

One question:

The field "META - Website description." is meant for Google search, right?

Like this?

If yes, it's not working

This field is meant to enter one or more of the listed options, but not any file or directory name, thus the answer to your initial question is NO.

https://www.seonative.de/meta-robots/
may be of help to get an idea...

there is a field for that, that's why I'm asking