What you could do is the "opera mini trick", AKA one beefy server, shared between many users, used to run heavyweight browsers. The pre-rendered DOM from these browsers could then be optimized and compressed, HTMX / Liveview style, and sent to the device.

The key insight here is that most smartphones are idle most of the time, so such a server (or group of servers) would need far less processing power than all the smartphones it replaces.

Given a Mitmproxy trace, modern llms could probably quickly build you simple apps for most popular services, leaving the heavyweight browsers for the long tail.