MariaDB v10.3 is currently the default version for Lando, but is no longer maintained according to https://mariadb.org/download/#release-schedule:

The current maintained versions are: 10.4, 10.5, 10.6, 10.11 (maintained for 5 years), 10.9, 10.10, 11.0, 11.1 (maintained for one year).