Remotely control a Mac that is connected to a VPN
Solution 1:
Consumer VPN providers have an app with some configuration choices. One such choice is whether all network traffic is or is not sent via the VPN.
If all network traffic is sent via the VPN (seemingly the obvious secure setting) then it really means ALL traffic is sent via the VPN and the computer will be logically separated from the rest of the local LAN. So local file sharing or screen sharing can't work.
Mullvad has this option. In Using the Mullvad app there is this screenshot:
Local network sharing needs to be enabled.