Help with older asus motherboard and EFI boot

So this week I got a new 1tb drive, I unplugged all my other drives and installed a new windows on it for testing. I removed it and plugged my all my drives including my ssd with my windows install.

Bios would not boot into windows, selecting windows boot manger it just kicks me back into the bios.

After reading up and trying to stuf like bootrec commands like /fixboot etc even rebuildbcd I could not get it to see my window. Then I came across bcdboot c:\windows and that fixed the problem.

Now I wanted to test something out.

I booted up just with 1 drive installed my old windows install on my 1TB ssd. After seeing it booted up fine I removed it(unplugged) and added the new 1tb format install windows, boot into windows restart to check if its fine. I then removed the 1tb with new windows install and put back my old ssd1tb. Back to bios not seeing the windows and me needing to use bcdboot to fix it.

Can someone exlain to me does the bios hold a boot table? Cause should it just not boot from the drive when its plugged in.

I know its a older EFI instead of UEFI board