Can t select users / groups for file/folder share

Nextcloud version: Storage Share 20.0.4
Operating system and version: Linux 5.4.0-56-generic x86_64
Apache or nginx version : ? (hosted by hetzner)
PHP version: 7.4.13

The issue you are facing:
I create new users / new Groups (Group share). Then I move to the folder I wan t to share with this new user. All old users / groups appear to be selected as soon as I start typing in the autocomplete field. But the recently created user does not appear. This worked until a few weeks. There have been at least one update of the nextcloud software from 19.0.x to 20.0.0. But it was already broken before this update.

Is this the first time you’ve seen this error? Yes
The output of your Nextcloud log in Admin > Logging:

No server logs "Everything is working fine"

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

n.a.

The output of your Apache/nginx/system log in /var/log/____:

n.a.

The problem was not the date of creation of the user or the group.

I had the option
“restrict users to only share with users in their group activated” (Settings -> Admin -> Sharing).

That is why I was unable to share the folder with the new user. She was not in any group I belonged to.

Credits for the Solution go to Hetzner Support :heart: