MariaDB 10.6 and the InnoDB that is no longer XtraDB

MariaDB replaced XtraDB with its own InnoDB fork some versions ago, and 10.6 is where the accumulated differences from MySQL stop being cosmetic.

-- MariaDB 10.6, but not MySQL 8.0
SELECT * FROM orders FOR SYSTEM_TIME AS OF '2021-06-01';
ALTER TABLE t ADD COLUMN c INT, ALGORITHM=NOCOPY;

-- MySQL 8.0, but not MariaDB 10.6
SELECT ... OVER w WINDOW w AS (...);   -- both, actually
CREATE ROLE ... WITH ADMIN;             -- syntax differs
-- and the JSON functions differ in return type

The two are no longer drop-in replacements for each other, and the places it shows are JSON handling, roles, and anything reading information_schema. An application supporting both needs a test matrix rather than an assumption, and most do not have one. System-versioned tables are a genuinely useful MariaDB feature with no MySQL equivalent, which makes them a one-way door worth entering deliberately.