Edit "search results" web part gives "SOMETHING WENT WRONG"

In my online SharePoint tenant I want to add a (standard) "search results" web part. So far, so good. However when I click "Edit web part" I get a "Something went wrong" message and a correlation id (I did sent this one to Microsoft but I'm affraid this will take some time, which I do not have).

What I tried:

- create a new empty page and placed the web part on it  -> same error

- exported a working webpart from another tenant and used that -> same error

- Different browser/different user/differen computer -> same error

When I do not try to edit the web part and just place it on the page, it works fine.

What can be wrong in my tenant? Is it some search setting? As you will understand, it cannot be a setting in the web-part, as I do not get the opportunity to edit a setting in the first place.

Any idea what might cause this issue?

Thanks, Mike