Been using Proton for over 4 years now, and have had no issues with it. I don’t use folders or tags that much, but if you are a paid member, you get unlimited of those. They recently announced calander invites (I personally never want to use them) and it looks like it should work fine. Proton also has unlimited aliases to hide your actual address, which I use all the time (coming over from SimpleLogin.)
The bundle (mail, VPN, calander, pass and drive) is really bang for the buck for what you get, even though you don’t use some of them. You can always upgrade to it later if you wish. And in case you don’t plan on paying, the free versions work just as you expect!