If you're using the admin_notifications app in NextCloud, please note it's been osbsoleted with Nextcloud 14 : itsfunctionality has been merged into the default notifications app for Nextcloud 14. You can safely uninstall and delete the "admin_notifications" app, because it does not do anything anymore.

Files bug report : Please update grauphel for NextCloud 15 · Issue #70 · cweiske/grauphel · GitHub

Followed bug report : NextCloud 15 compatibility for files_trackdownloads

Filed bug report : Please udpate caniupdate for NextCloud 15 compatibility · Issue #25 · nextcloud/caniupdate · GitHub