Good news for MySQL users wishing to upgrade to MariaDB: MariaDB 10.5.7 onwards understands formerly-incompatible MySQL JSON fields! This blog entry explains how to install and use them.
Starting from MariaDB 10.5.7 (commit f6549e), it is possible to upgrade from MySQL 5.7 tables containing JSON by loading the MYSQL_JSON data type plugin.
MariaDB and MySQL JSON formats are not the same. In MySQL, the JSON type is a native type, while in MariaDB JSON is just an alias for LONGTEXT. What this means in practice is that data in JSON format are not compatible with each other.