Here: https://dev.mysql.com/doc/refman/8.0/en/insert-on-duplicate.html

Oracle declares the use of VALUES() to be deprecated in statements like this.

INSERT INTO tbl (id, col) 

  VALUES (1,'value')

ON DUPLICATE KEY UPDATE col=VALUES(col)

In their 8.20+ they specify the use of aliases like this.

INSERT INTO tbl (id, col) 

  VALUES (1,'value') AS alias

ON DUPLICATE KEY UPDATE col=alias.col

It would be helpful (to the WordPress project among others) to avoid needing two different syntaxes in order to support both MariaDB and MySQL.