I got Roon working over VPN very easily using the Softether VPN server on windows 10 which is running on the same machine as the Roon Core server.
I’m using the standard L2TP/IPSEC VPN client settings that are built into both IOS and Android with no problems.
Im using Google Wifi Mesh network at home behind a broadband router in bridge mode, so I just had to add some port forwarding rules for the VPN server and that was it.
It even streams dff and dsf 352 DoP files without resampling or any stuttering.
I do have 100Mbit/40Mbit network that helps a lot with that! (40Mbit out from my house)
If anyone is interested I can create a video guide and screenshots.