Is there an application similar to NetMod VPN Client in Linux?
ProtonVPN?
Looking at their link, NetMod is JUST a client, rather than a service. It's something they could use to VPN into his home network, given a means set up for it. Proton is JUST for accessing Proton's general purpose VPN service, and doesn't have the feature set NetMod does. I'm sure there IS such a thing, but I don't know of one, and my search results are polluted with "top ten VPN services!" junk. >_<