I don't love paying for subscriptions either or carrying water for any company in an unpaid role...but is it true that if you don't subscribe, you get locked out of any of your events/calendars?
From what I've seen and understand, you lose access to some "enhanced" features (who's value can certainly be questioned/rejected), but your calendars/events aren't held hostage to the subscription the way you imply here.
Well, I certainly didn't spend hard earned cash for an app so they could constantly nag me to hand them more money. Flexibits can pound sand. I cut my losses, and wrote off what I spent on their software. They will never get another dime from me, even if they manage to cure cancer and COVID in the same week. Their "business model" has earned them a special place in developer hell.