[Quoth]

That will be deemed illegal misuse by most ISPs and I doubt it will work well on Mobile. I used to work for an ISP.

Hosting with rsync will work on anything. Cloudflare Tunnel is a stupid solution for self hosting and it's designed to mitigate DDOS and hide where you really are. For the tunnel to work without port forwarding across NAT it's essentially creating a virtual site on a Cloudflare server and using a sync process on your LAN. There is no other way for it to work.

It's breaking T&C of any domestic ISP contract I've ever seen, especially 3G
/4G/5G services.

The only thing I ever self hosted was a VPN server on my LAN and its port was forwarded to 80 and 433. Then using a VPN client at a public WiFi I could safely access my email via my home internet. My two sons used it also at university as only the University email worked and all ports except for web browsing were blocked. Since that was personal use by the people living here it didn't contravene T&C. Our home internet was 8 Mbps down / 1 Mbps up (typcally 7.4 Mbps & 0.95 Mbps), so the VPN gave 1 Mbps download and 8 Mbps upload to the home LAN. It was DOCSIS (cable protocol) over a 13km microwave link. I shut it down in 2010 when I stopped travelling.
Now we are on fibre and it's 500 Mbps down and 50 Mbps up. Speedtest just now gives download 554.18 and upload Mbps 55.34, but the T&C still forbid self hosting, which other than a secured VPN for you own private use of email and banking out on a public Wifi is a mug's game. Public WiFi can have MiM attacks on HTTPS.