i have the same issue. same OC version. i upgraded few weeks ago and everything was fine until a few days ago.
log can be provided. thx in advance.
Update : after reading the logs i realised there was an app at the origin of the issue. so i went disabled :
- Two-Factor Authentication via Nextcloud notification
- Two-Factor Gateway (this is the issue in my case)
- External storage support for Google Drive (this didnt seem necessary but wasnt using anyway)
now when click on Overview for Admin page is available. still OCC app doesnt work so i think i have to work on that.