It's pretty easy to self-host CalDAV and CardDAV. I went with Baïkal, it took me maybe 15 minutes to install on a server, it's supported by all of the calendar tools I use, and it's worked perfectly fine for a few months now. So now I'm completely free of Google.
Maybe not for everyone, but a way more feasible option than most people seem to realize.
Yeah I've investigated it a couple of times but never pulled the trigger with self-hosting. Could run it on my rpi and access via Tailscale, but seems like something that should be provided by the email provider that I pay money for. They also do have Contacts and Calendar products, but they're completely self-contained and apparently can only be used by protonmail which is mostly pointless.
Maybe not for everyone, but a way more feasible option than most people seem to realize.