Yeah I definitely wouldn’t run plex on Cloudflare Tunnels. It would be worse than a traditional VPN, Tailscale, or even just opening up a port, as you are bandwidth limited over Tunnels.
Mainly I use Tunnels as a reverse proxy for any web apps I’m hosting. One example is my Minecraft server management portal, plus a few development sites.
You can also use Cloudflared as a VPN (kind of), using WARP as the client. There’s limitations with it, and in my testing it’s much slower than any direct VPN connections.
For sharing amongst friends or family, Tailscale is the better solution, the free tier is insanely good for what you get.