I would use a Live USB with EndeavourOS on.
Boot it up in Legacy/CSM mode.
Plug in the USB drive you want to install EnOS on.
Start the installer and make a “erase and install” installation in MBR mode onto the connected USB drive.
Choose the MBR of the connected drive as the location for installation of the bootloader.
This could be a bit tricky if those are using different CPUs and/or GPUs, as far as I know, needing different microcodes and drivers (proprietaries for nvidia cards for example) etc.