I've lost a little hair diagnosing this - I didn't have it to lose.
My office location's IP has been allowed to pass the firewall of a remote VNC server. So if I need to access the remote location I have to do it through my office router.
I have a Wireguard VPN connection to my office. The remote IP is allowed to pass through the Wireguard peer config. Yet I simply could not get TurboVNC to connect. Checking packet logs I see no traffic coming from my PC to my gateway.
I've been checking every network config I have and second, third, and fourth guessing myself trying to figure out what's broken. Finally, on a whim, I tried a different VNC program. It worked.
I'm running Windows 11, TurboVNC x64 v3 (previously 3.0, now 3.0.1). I don't know what else to share or what else to check to resolve this.