It is using a different socket than before. You might have to edit /etc/phpMyAdmin/config.inc.php accordingly. Remember the file is generated from templates.
socket at localhost: /run/rh-mariadb105-mariadb/nextcloud-mysql.sock
https://docs.phpmyadmin.net/en/latest/config.html
Example on how to use multiple servers (and/or sockets I guess):
https://docs.phpmyadmin.net/hu/latest/config.html?highlight=multiple#example-for-using-multiple-mysql-servers
cc/ maybe @stephdl has some other advice.