Mariadb can not find system tables

I am running MariaDB 10.3.27 and after an erroneous long query MariaDB stopped working. I restarted it and checked systemctl status. MariaDB was working but also have the below errors:

-none
[ERROR] mariadbd: Event Scheduler: An error occurred when initializing system tables. Disabling the Event Scheduler.
mariadbd: 2021-09-30 19:44:58 1 [Warning] Failed to load slave replication state from table mysql.gtid_slave_pos: 1146: Table 'mysql.gtid_slave_pos' doesn't exist
mariadbd: 2021-09-30 19:44:58 0 [Note] Reading of all Master_info entries succeeded
mariadbd: 2021-09-30 19:44:58 0 [Note] Added new Master_info '' to hash table
mariadbd: 2021-09-30 19:44:58 0 [Note] /usr/sbin/mariadbd: ready for connections.
mariadbd: Version: '10.5.10-MariaDB'  socket: '/var/lib/mysql/mysql.sock'  port: 3306  MariaDB Server
systemd: Started MariaDB 10.5.10 database server.
mariadbd: 2021-09-30 19:44:58 3 [ERROR] InnoDB: Table mysql.innodb_table_stats not found.
mariadbd: 2021-09-30 19:47:20 0 [Note] InnoDB: Buffer pool(s) load completed at 210930 19:47:20
mariadbd: 2021-10-01  6:29:22 14690 [ERROR] Column count of mysql.proc is wrong. Expected 21, found 20. Created with MariaDB 50565, now running 100510. Please use mariadb-upgrade to fix this error

Well, I think this is very bad. I can see that I am suggested to run mariadb-upgrade, but I am afraid that this would break things. I also don't understand why I have suddenly to upgrade. It worked fine before the long running query.