Mysqld doesn't start

Quite a while ago I upgraded to TOS5 which didn’t work well so that I rolled back to TOS3. Afterwards I was happy that the Omnia worked again but never started installing nextcloud for example.

My mariadb-server can’t start:

mysql -u root -p status
Enter password:
ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘/var/run/mysql.sock’ (2)

I don’t have the file /var/run/mysql.sock.

Reinstalling mariadb didn’t work neither does restarting or starting mysqld:

mysqld restart (or mysqld start)
2021-05-13 13:39:52 3069654012 [Warning] option ‘table_open_cache’: unsigned value 4 adjusted to 10
2021-05-13 13:39:52 3069654012 [Note] mysqld (mysqld 10.2.18-MariaDB) starting as process 21917 …
mysqld: Please consult the Knowledge Base to find out how to run mysqld as root!
2021-05-13 13:39:52 3069654012 [ERROR] Aborting

The owner/group of /srv/mysql ist mysql:mysql, mode is 0700.

Sorry, I don’t know where to start. I had a running database for kodi and nextcloud, both I didn’t use for a while but would like to use it again. I can’t even check if the db’s are still there. It might have to do with the above mentioned rollback.

Thanks to everybody for any hints and help!