After upgrading to NC29(30), creating a folder or file in a group folder (for ldap group 1000+ users) has noticeably slowed down

Steps to reproduce

1. Create a group folder.
2. Set access to it for ldap group of users more than 1000.
3. Create a "new folder" in the group folder.
4. Delete the "new folder".

Expected behaviour

The folder will appear almost instantly. And will disappear after deletion in the same amount of time.

Actual behaviour

The folder will appear in 4 seconds. It takes the same amount of time to remove it.

Server configuration

Debian 12
Nginx 1.22.1
Postgresql 14
PHP 8.3
NC30
Group folders 18.0.9
Updated from an older Nextcloud/ownCloud
NC installed on KVM with nfs mount for "data" folder.
External storage: local, smb
encryption: no
External user-backend: LDAP

Client configuration

Chrome browser
Debian 12

If you enable the activity option 'activity_use_cached_mountpoints' => true, then you have to wait 3 minutes or refresh the page. However, the flag for notifying changes in the group folder is not checked by default for most users.

Folders and files should be created as quickly as in the root directory.

Start by reproducing creation and deletion in a group folder shared with an LDAP group of more than 1,000 users, and compare the timing with the root directory. Investigate the group-folder handling around mountpoint changes and the activity_use_cached_mountpoints setting. Done means both operations complete with root-directory-like responsiveness without requiring a refresh or waiting several minutes.