I’ve used Termux with proot-distro to install Debian with xfce4 on my Android phone.
I can use it on a monitor with a usb-c to hdmi cable, or just vnc into it from a PC, or use the phone itself with RVNC to have a desktop “in hands”.
Sensor data is sadly not working properly, so no CPU usage and temperatures are a bit off as well.
XFCE really is it isn’t it? I first tried it when I got my CDs in the mail for Mandrake/Mandriva Linux back in 2002 or so and am still using it today!
Hoping for Wayland support soon
How?
As OP said, you use Termux. You can use AnLinux or Andronix for easier setup with Termux. You will likely also need a VNC Viewer to actually see and use the desktop. It’s been a while, so I don’t recall exactly how to do it, sorry.
You can install Termux from the F-droid store, which is a Android terminal emulator and Linux environment. Then install the proot-distro package and you can install stuff like Ubuntu, Debian, Arch…
you dont even need a rooted device.