I've had remote access working on my plex server for years but yesterday it stopped working. My ISP uses CG-NAT but that hasn't been a problem until remote access stopped yesterday. To be perfectly honest I dont kbow how it's been working as from what I understand it shouldn't, but it has been. The server is running on an Intel Nuc that uses Mint. I've been using it both to listen to music and watch media without fault from friends/family homes and my phone remotely. Everything works perfectly inside the network but nothing remotely anymore.
I've tried both with and without a port forwarding rule on my router. I have pihole running on the same nuc which I've tried both disabling and removing from the routers dns handling. I didn't think this was the problem but I at least wanted to rule it out.
Im fast running out of ideas as i can't understand what's different from before. The only thing that's changed on my network is adding a new Switch 2, besides that everything is exactly the same.
If anyone has any suggestions I'd really appreciate it!

I forgot to add that I have a lifetime plex pass

I gave up in my lifetime Plex pass and switched to Jellyfin. I haven't missed it constantly getting worse and advertising their products on my server. I know that doesn't fix your problem, but I think your time is better spent on migration than fixes.

I had this happen to me too. For some reason, my Plex tunnel kept working for a little longer after my ISP enabled CG-NAT. Sometimes you can contact your ISP for a static IP but the solution to this is to use a tunnel of some sort, like a Cloudflare tunnel or Tailscale or a NGINX reverse proxy on a VPS provider like Hetzner or IBM Cloud or AWS Lightsail.

I can get a static ip but it's £8 a month. I could tolerate it but I've been with this isp for I think a year now and it's been using CG-NAT the whole time. It has been working the whole time! This is what is driving me nuts, it has been working with no issues for a long time and suddenly it doesn't.