I have a Google account that I created with a throwaway non-gmail email account. I don’t use the email or the Google account for anything else. I then sync my required Google calendars to that (my partner still uses Google, so does my union and my work), and I sync that account to my phone with DAVx5 and to my computers with vdirsyncer (eventually pimsync, when it makes it to nix home-manager) by setting up Google CalDAV API credentials as explained here.
I have to use a local calendar app on each device to see my Google calendar with my NextCloud calendars, but it’s the best that’s possible, I think.
fascists gonna fascist