Yeah its read only, but I don’t have to edit the calendars I’m subscribed to, so it works for me.

But it would be mildly annoying if I had to edit stuff in those. I’m not sure how that would work in the first place. In my case Microsoft would have to have some sort of API, even if its just CALDav, so Nextcloud could submit the changes you make. Does Microsoft even allow for something like that?

I’ve gotten the calendar to subscribe to external calendars. One work related Microsoft calendar, and one for holidays.