I have added the following simple test event on my mysql database via phpmyadmin:
CREATE DEFINER=`root`@`localhost` EVENT `my_event` ON SCHEDULE EVERY 1 MINUTE
I just figured out that on MariaDB, after adding an event (in my case, it was the first one), you have to restart the event-scheduler
SET GLOBAL event_scheduler = OFF;
and then
SET GLOBAL event_scheduler = ON;
to make it actually bring the scheduler into "waiting for activation"-state.