Actual is libre and gratis

You should still be able to access everything through tailscale once you switch everything over to use local IP addresses.

Is that unique to Joplin?

Agreed, if from a corporation. FOSS services are usually also gratis, and can be compiled from source if not.

You can block instances yourself, I personally don’t like when an instance makes that decision for me.

Fair enough :)

Is Boost really that much better than Eternity or Voyager that you put up with ads?

Just self-host a VPN on a VPS so you can enable disk encryption and disable logging.

I was using proton for a while, but they are pretty expensive if you want features like catchall and more aliases, on top of restricting clients.

Migadu offers complete email freedom for $20 ($10 for students) a year, unlimited accounts, aliases, identities, etc. I’ve been very happy with them.