Fastmail has a pretty good calendar when you get subscribe for email. My main complaint is who don't use embedded calendar links and instead send you .ics files or force you to use Google Calendar.
I migrated emails to Fastmail a few years ago, but have been holding on to Google Calendar.
> Android does not support CalDAV natively, however you can easily add support by installing a CalDAV sync adapter. We have tested and recommend DAVx⁵, which is approximately $5. Once you have added your account in DAVx⁵, you can use the native Android calendar or any other calendar app and the changes will sync with Fastmail.
https://www.fastmail.help/hc/en-us/articles/1500000279881-Se...
It also covers contacts integration too!