How to restore normal operation of Nextcloud after an unsuccessful update?

Question

ownCloud/Nextcloud

Hello!
I made a mistake in the Nextcloud settings to set the Beta update channel instead of Stable, after which I started the update. After completing the preparatory steps, I updated the page in order to directly launch the update itself, but I received an error 500, which I could not fix by picking .htaccess and torturing folders and files with their rights. I decided to roll back, opened the folder with the backup, which was made automatically during one of the automatic preparatory steps: nc_data/updater-oc1fk6a2ia69/backups/nextcloud-16.0.5.1 and returned its contents to .../web/
As a result, the authorization form works, background synchronization tasks (WebDAV), access to storage through applications. Can't log in.
Almost everything in the web interface stopped working. Here is an example of what is seen in the window when one of the users logs in.
There is no possibility to launch applications, settings, etc. The disk full indicator for other users (who have files) displays reliable information. That is, it turns out that the system seems to be functioning, but the system management web interface does not work.
Used by Synology Disk Station (Disk station manager 6.22-24922)
Appache 2.4
Php 7.2
MariaDB 10
Please tell me what to do so that everything works as before.

Answer 1

The simplest solution to the problem is to save contacts and calendars on synchronized devices, completely reinstall NextCloud and then import contacts and calendars. User files remained safe and sound on the server.

Answer 2

call the admin