Google had removed my X server app from Play Store, because it was too old (is 2022 too old?)
But no more! I have recompiled it for the newest Android version and published it back. And you can use it to run GUI apps from Termux. Launch X server first, then run these commands in Termux, then switch back to X server:
pkg install x11-repo
pkg install xfce4
export DISPLAY=127.0.0.1:0
export PULSE_SERVER=tcp:127.0.0.1:4713
xfce4-session
Termux now has it's own X server, my app is pretty similar, except that it's landscape by default.