The problem is the common user wants thing to just work.

I work at a major university. At our science department we tried using 'https://www.horde.org/apps/groupware' for calendar. But fails randomly, refresh issues. The computing centre claims they have everything fine. Groupware has so many bugs. The IT department cannot fix these.

Note that every self-hosted nerd will claim they do everything with nextcloud with RPi and all is perfect but it does not work for 100 people.

At the end we moved to Google calendar. Everything just works.

For us, contributing to science is important than being 100 % open.

Before you say iCloud it is much worse at losing mails/calendar sync - BTW, try it with > 20 users... Microsoft is kinda OK but works painfully when using linux or mac devices.

It is unfortunate people complain about FAANG without providing replacements.

The concept of auto-sharing calendars with each other is fundamentally wrong anyway. Why enable all this snooping? Especially with know third party offenders.

Edit: I use a paper calendar. Works flawlessly.

To plan meetings with colleagues and such? Remind you when meetings are about to start, have links to online meetings?