Newly installed nextcloud doesn't show login windows


I just installed nextcloud to a raspberry pi4 with Ubuntu 20.10. Followed this guide:

I installed nextcloud successfully earlier and the user and the initial page was already strange. Simple black and white background and slipped away instead of the correct blue one. After creating the user and connecting to the MariaDB I got the logon page without the possibilty to logon:
I tried it from different browsers and device with the same result.