the notifications of foundation.e.calendar will not be generated by microg at all, it’s a system facility. If the event is in the calendar, it should get a reminder.
I haven’t experienced this myself (I get notified on time), but there are some reports on Calendars and notifications:
- Missing notifications of several apps (since cleared)
- Calendar notification
Fastmail: unsure if this is related. Only if notifications do not work at all and are overriden by Do-not-Disturb settings?