I'm running a small Caddy + Rust (Actix Web) service on my Raspberry Pi 2B. Not the snappiest service ever but usable. Part of the slowness might also be the fact that it's online using Cloudflare Tunnels.
Basically, you can have a computer available online through Cloudflare without having to open any ports, as it makes the computer available through outbound connections. Should also make it possible to host behind CGNAT.