If it's openvpn you can just port forward from your router to the RaspberryPi's internal ip address.

If it's a webserver you can do the same, or use something like Cloudflare tunnels to expose the service.

> How do you expose the Raspberry Pi so that you can reach it from the outside internet?

I had this issue recently trying to enable port forwarding on a comcast router, which is no longer allowed.

Turns out the answer is "stop the router from blocking ipv6 connections". You can just connect directly to whatever device you want over ipv6.

Port forwarding in my home router. I have it forwarded to 53 UDP since some public networks have firewalls, but the DNS port is almost never blocked.