As a prove of concept I am running the following combo:
- pixel 6 pro
- enabled developer option
- activate "simulate second display"
- enabled "force allow apps on external"
- enabled "force activities to be resizeable"
- enabled "enable freeform windows"
- enabled "force desktop mode"
At this point I connect phone via usb to either my laptop or raspi and start scrcpy targeting external display.
In 1080, things work well even with raspi, the lag is minimal. 4k requires compromise with refresh rate and bit rate.
For now I am playing with browser and termux. Both give a reasonable user experience.