I use nextcloud. You log into the MacOS reminders application with your nextcloud CalDAV address. For Android syncing you can use jtxboard.
For notes I use nextcloud notes on the phone and an application called "Notable" on macOS.
MacOS also allows you to sync contacts via nextcloud as well.
Highly recommend taking the time to set up your own self hosted server if you like the convinence of an "ecosystem" while maintaining some semblance of privacy.