Running a VPN client on Windows 10, how do I manually add a route to the routing table so that I will always be able to connect to a PC on my network?

Running a vpn from your desktop means that all network packets get routed via the vpn. If you want to access the local network you need to implicitly allow local network access from within the vpn software. setting a route within windows won't work as the vpn is handling the data packets to the network.

in wireguard this is easy, you can edit the tunnel and there's a checkbox you can unset to allow local traffic, not sure which vpn you use though.

see pic