Gitlab REST API endpoint "avatar" always returning gravatar url

Since a while it's not possible to fetch the user avatars anymore. The files are now only accessible via Session cookie (there are already multiple issues for this topic).

Therefore, I tried to use the REST endpoint avatar. But I always get the gravatar-url instead of a url I can use (or download from).

Is the endpoint broken or am I missing something obvious? I tried via the browser being logged in to my self-hosted Gitlab. So auth shouldn't be the issue.

Thx! Ronny