You do not need to port forward to share a Plex instance over the Internet. App.plex.tv manages the inbound connections automatically. All you need to do is manage invites to your friends. They log in with their email/password or with Google SSO to app.plex.tv and your content will be available over a secure connection with no port forwarding.
At one point I had been playing GTA V online pretty consistently when I had a cheater start targeting me. It was pretty frustrating and after 30 minutes of that I gave up and closed down for the day. I shifted my attention to other games after that. I definitely get that they want to stop cheaters - cheaters ruin the fun for others. It’s a shame that the new anti cheat has made it so that Steam Deck players are stuck unable to play online.