Your best bet is probably PostmarketOS, its not debian but alpine, but does support the phone and aparrently still gets some updates.

Theres a link on the page to the non T variant with flashing instructions.

https://wiki.postmarketos.org/wiki/OnePlus_5T_(oneplus-dumpling)

It should work as long as it can reach the internet

I’m not really a fan of cloudflare tunnels, but I guess thats an option too

You can’t expose ports on mobile data. You can ether host the web server at home or on a vps or use something like tailscale.

You could try tunneling usb from the host into wine with usbip, but I have a feeling that this wouldn’t work

I use traefik, but caddy should work too. I can share the docker-compose files I use later.

I didn’t understand the docs either, that’s why I’m using https://github.com/girlbossceo/conduwuit insted