When I activate MullvadVPN on Whonix Workstation, the system is unable to access the Internet due to interference from the Workstation firewall. I was able to verify this by deactivating the firewall in the Workstation terminal with the command sudo systemctl disable whonix-firewall and then trying to access the Internet again, and this attempt was successful after deactivating the firewall. However, to avoid compromising the security of the Workstation, I do not want to have to deactivate the Workstation firewall in order to access the Internet while connected to MullvadVPN, and so I would like to know how I can configure the Workstation firewall to allow Internet access with MullvadVPN enabled, specifically through OpenVPN in TCP mode and on port 443.
Unfortunately, that’s unsupported.
Two different firewalls interacting with each other is difficult to implement.
You could post a feature request against Mullvad, but I guess chances that they will implement this are low because they didn’t fix/implement https://github.com/mullvad/mullvadvpn-app/issues/3803 either.
So unless you’re paying a third party developer to fix this (no recommendations are provided), very most likely this won’t be fixed anytime soon.