It's not a solution for non-technical people, but can you use Cloudflare Zero Trust or similar for Plex?
I have my own Subsonic music server at home, using Navidrome. I set up Cloudflare Zero Trust so I can access it remotely via the web, with a secure Google login in front of it. You can use other authentication methods, it doesn't have to be Google. Passwords, 2FA, certificates, other providers.
For desktop, any browser works. For mobile I use Symfonium. It's not free, it's a cheap one-time purchase, but it works great with that set-up and means I can stream my music anywhere, without the need for a VPN.