I have 2015 MBP, that i bought with no screen, just the bottom case. I use it with my
pretty much useless 27" thunderbolt display.
MBP did not come with a SSD and it was never updated past sierra as it missing the firmware.
High sierra can see my nvme drive and format it and install to it but when it reboots it cannot
finish the firmware update. I have another 2015 MBP fully functional with a original apple ssd
it runs Monterey and bootcamp windows 10. I thought I'd be sneaky and stick that drive on the
other mbp and trick it to updating the firmware, NOPE.
I don't really feel like buying apple SSD to get this done as it negates the good deal I got on an
a nvme drive.

SO.... i was thinking of cloning my known good ssd or doing a TM backup. Then erasing the apple SSD
installing it on the non updated MBP and install high sierra so it will update the firmware.
Once that is done switch back to the nvme and proceed with an fresh install and then restore my apple ssd for
my working MBP

Is that a plan or am i completely wrong and "do I even apple"

yes i have read the wiki on compatible ssd and gum stick adapters, im good on that.

Any help is appreciated and razzing also welcomed.