From MariaDB documentation:

In MariaDB 10.4 and later, the mysql.global_priv table has replaced the mysql.user table, and mysql.user should be considered obsolete. It is now a view into mysql.global_priv created for compatibility with older applications and monitoring scripts. New tools are supposed to use INFORMATION_SCHEMA tables.

Either this is a documentation bug or a missing feature, since it is not possible to retrieve all privileges stored in mysql.global_priv via INFORMATION_SCHEMA.

Proposal:
Add a view INFORMATION_SCHEMA.GLOBAL_PRIVILEGES which returns values from mysql.global_priv in a human readable form. This will avoid to write a complex view for retrieving the privileges in client applications.