For the record, I'm facing the same problem using both SQuirreL SQL 4.3.0 and snapshot-20220227_2203 against MariaDB 10.5.15; the old stable driver version 2.7.5 of the Connector/J does not work for me. However, the 3.0.4-SNAPSHOT (see here and here how to obtain it using, e.g., maven) works.
For the record, I'm facing the same problem using both SQuirreL SQL 4.3.0 and snapshot-20220227_2203 against MariaDB 10.5.15; the old stable driver version 2.7.5 of the Connector/J does not work for me.