Maybe buying a single seat enterprise license of Microsoft365 might work for you. Microsoft treats enterprise clients very differently than end users. Only (potential) down side is that you will have to set your own security policies and manage a bunch of things that go beyond a calendar. There is a bonus though. A single enterprise seat license includes 1TB of private-ish enterprise cloud storage.
I tried this and found that at the time there were massive limitations. Admittedly it was a few years ago, but they didn't make it simple to just have a forwarding mail group so that I could have a shared mail address/distribution list to myself and my wife forwarded to our inbox, and you basically had to have a shared email box that was separate to your primary. It didn't pass the spouse test considering this is a basic feature that everyone has so it didn't make it past the trial.
I was actually surprised at how limited the 365 was, I don't remember the other limitations but they seemed fundamental.
Yes, it could very well fullfil my requirements, but preferably a bit more simplistic. Like Proton Calendar, if only it integrated into the iOS ecosystem.
Idea #2. Why not just use apple’s iCloud with advanced data protection turned on? It’s not perfect from a privacy perspective but at least apples business model isn’t data mining you.
Actually, I was looking in the direction of smaller european gpdr focused companies, but this is actually a really good suggestion. I will look into it! Thx!