Search in user list does not search display name and email

I have a lot of pupils registering. I have to put them in different groups (classes). I would use search in user directory for it but it will only search for user name but not display name or email.

Username: frank
Displayname: Frank Drevin

Search will only find if I search “frank” but not drevin nor company.

My workaround would have been to use browser search (STRG+F) but this will also activate NextCloud search which does not work.

Any hints?