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?

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.