MariaDB/MySQL upgrade instructions begins with

SET @@max_execution_time=0;

On MariaDB 10.5, this fails with:

ERROR 1193 (HY000) at line 1: Unknown system variable 'max_execution_time'

For MariaDB, the correct statement is max_statement_time. MySQL used to have a variable of this name before renaming it max_execution_time.

As per https://mariadb.com/kb/en/system-variable-differences-between-mariadb-10-5-and-mysql-8-0/:

max_statement_time

Description: Maximum time in seconds that a query can execute before being aborted. This includes all queries, not just SELECT statements, but excludes statements in stored procedures. If set to 0, no limit is applied. See Aborting statements that take longer than a certain time to execute for details and limitations. Useful when combined with SET STATEMENT for limiting the execution times of individual queries. Replicas are not affected by this variable, however, from MariaDB 10.10, there's slave_max_statement_time that sets the limit to abort queries on a replica.
Commandline: --max-statement-time[=#]
Scope: Global, Session
Dynamic: Yes
Data Type: numeric
Default Value: 0.000000
Range: 0 to 31536000

Since default value is 0, it's only applicable to instances where max_statement_time variable was customized.