I disagree. The is a distinction betweeen read-write and admin permissions.
The owner has, obviously, admin permissions for a library. Another user posses admin permissions only when the library is shared with admin permissions.
The admin permission level exists in Seafile Professional. It does not exist in Seafile CE.
I saw in your screenshot that your file names contain German words. So I assume you speak German. Please find more info here: https://de.seafile.com/support/benutzer/anleitung/seahub/bibliotheken-und-ordner-an-andere-benutzer-freigeben/