It remembers which physical port we're using. Hmmm... tricky.
If I do not enter UEFI, most of the time this computer will boot from the eMMC.
When I go in to change it, it is not saved indefinitely, like old computers with a dead CMOS battery.
I assumed going out of Windows S mode would fix it, but the default boot order is preserved.
I prefer usually to leave the internal bootloader alone & boot from USB. I have one old laptop with an internal XP bootloader including Linux, but I have not figured out if it is possible to boot Linux w/Win7 & later bootloaders.