The blurb says "calendar sharing" but the price comparison has calendar sharing unticked for the free version. Guess I'll just try. No cost to do so.
It does seem to work only with client apps, no web interface, and I have had fits just trying to get people to adopt Signal. Many are locked into WhatsApp and FBMessenger. Ouch.
Anyway, that's FWIW. I am Google-free with bundled Apple apps and a boatload of Free and OpenSource apps. I use apple and comcast mail.
Apple office apps are all MS compatible as is Libre Office.
I try to do nothing "in the cloud" since any information that leaves the home is, IMO, subject to loss and seizure.