got bored and used the Terminal to see if my desktop PC's are UEFI or BIOS.

[Moltke]

Yes... I should have added -- the current OS installed -- not whether its supported..
You installed the BIOS version - no efi folder..
Does not represent if UEFI is supported or not...


The other commands as you post would.. 

Yes, that's what I thought. I was at first confused but then I remembered all that problem I went throught with W10. I found this article https://www.pcsuggest.com/check-bios-uef...-in-linux/ which among other things states that

Note: The above method (ls /sys/firmware/efi or efibootmgr) works only if the system is booted from a UEFI bootable media, else it behaves like an older legacy BIOS system.

Learnt a few new things