As an alternative or enhancement of reminder emails, give users the ability to add blocking to their calendar, appropriately timed to content if it varies, via the UI (Learners portal)
Extra points if it can use the existing M365 API link to inject this as phishsim is already done.
I find myself getting busy and never launch the training myself when the notice is issued (that I configure for our org and customers!) - then I scramble at the end of the month to block time so I get it done. Save me from my lazy & poorly coordinated self, please! :)