I don't understand the Sata Mode setting in the bios M.2 or Sata Express. I would think a M.2 drive such as the Samsung 970 Evo NVMe M.2 would be set to M.2, no? Because when I try to save and exit when setting that setting to M.2 it always reverts back to Sata Express, why? The Samsung Benchmark shows it:

So it appears to be working correctly but.... The PC doesn't really boot any faster than the old Intel 320 series (a measily 3 seconds faster) so I still feel I'm missing something and it isn't running correctly.
Also I read that a M.2 NVMe drive isn't bootable when set to MBR and has to be set to GPT but mine is set to MBR and boots just fine?