You would set up the allowlist in your firewall. There are plenty of free options for dynamic DNS though not from any ISPs that I’m aware of.

Perfect use for allowlisting based on dynamic DNS hostnames.

Unreliable how?

This is only good news for the people at Skiff that are getting paid. Skiff is dead.

For what it’s worth, there are some options on flathub.org even if they aren’t official.

Uh yeah… they’re not finishing in the top 4. That should be obvious at this point.