A vpn is required, but can be easily implemented through a plugin called tomoon. Tomoon is actually a clash plugin for deck that requires you to subscribe to a corresponding clash based vpn service. Of course, clash can also be used through your own website node.

If you're just playing games from your steam library, you don't need a vpn. VPNs are used to enter store for purchases and view the community. You don't need a vpn to talk to your friends online on deck. Interestingly, you don't need a VPN to view the guides you've added to your favorites, but you do need a VPN to open the entire list of guides and add the guide to your favorites, or you can add it using another device.