Rooted phones: Run the Ubuntu filesystem through chroot.
Non-rooted phones: Run an app-private native Termux userspace and install desktop packages from the X11 and TUR repositories. PRoot is not used.
Rendering: Both modes connect directly to the embedded X11 server on DISPLAY=:0. Adreno devices use Turnip/Zink hardware acceleration when available; other GPUs fall back to Mesa software rendering.