Big revelation thanks to your explanations to educate me. I wasn't holding out (hiding information), but I left out a significant piece of the puzzle because of my recently amplified fear about Win7, and having that previously as a dual boot option.
That is the key point, and a picture tells the story that has been confusing you and me, and I CAUSED the confusion.
Recall, the history of this PC1 as originally a Win7 machine (full retail pro license), to which I added a second machine (full retail pro license) as a dual boot with the W10 being the primary/default boot option.
However (the big fat however), the BCD table resided on the Win7 drive denoted as an EVO850.
For all of our diagnostics, I had never plugged in this Win7 drive for fear of installing drivers etc. and being open and exposed with a network connection to viruses or other malicious actors, so we were not able to see the critical FAT32 partition which was on that drive.
In following your recommendation (Post 23) to investigate the two drives offered for Redeploy and find out their manufacture/origin etc. via the restore menu; I thought, why not look at all the drives relevant drives? Even the Win7 drive.
Upon plugging in the Evo850 Win7 drive and rebooting, I was back to my standard (3) boot options menu: Win10, Win7, Rescue Media.
My sincere apologies for not thinking through (too cautious about Win7 is my excuse).
The obvious gaping hole (mistaken information) was my stating/thinking the W10 boot SSD was in fact a full-up valid W10 installation -- without the BCD FAT32 partition it isn't/wasn't.
I also went far enough in my investigations with the the Win7 drive active to see that I was running MR v7.3.5925.
So, if I had had the presence of mind to create an external Rescue Key on USB/CD/DVD I would have been in better shape at the start of this MOBO failure recovery campaign.
The only obvious problems with running my dual boot system as it stands now are: the vulnerability of Win7, and the network drivers for the new MOBO are not installed.
I do have some old software that is operable on the Win7 machine, and I likely need it too be able to look into some extensive archiving of business etc. that I did over the years.
You've got me convinced to drop the dual boot on my main Win10 PC -- and put the Win7 on another air-gapped PC build (use scraps of old PC, buy a used MOBO, cobble pieces together).
I could always go back to my dual boot backups as long as I preserve the files as archives somewhere (say independent of my new PC3 backups)
I say this, because there may been some usefulness to have retained the backup images of the dual boot Evo850 drive for the fab of the Win7 only machine.
That leads me to next steps for the Win10 machine we have been trying to recover.
If I've understood your recommendations correctly I can redeploy to the EVO970 m.2 drive which is drive 3 in the prior redeploy menu, or GPT disk 4 in the image above.
Correct me if I am wrong, Redeploy is smart enough to fill in the FAT 32 BCD on the EVO970 m.e on its own, it does not need BCD info off the EVO850 Win7 Dual Boot drive BCD.
So, I should:
unplug the EVO850 Win drive,
in the Redeploy menu select the SECOND item listed as Windows Pro (1) for the redeploy and start the redeploy
(Note: do NOT select the 1st item which was the previous Win10 EVO 860 SSD install without the FAT32 BCD).
Chose drivers (especially for the LAN from the MOBO CD (alternatively, may have to use this PC2 to get valid current drivers later).
Run Fix Boot Problems if/as applicable with Fix Boot Menu
Check UEFI settings. Suspect the EVO870 m.2 will still show NVME (not SATA). Not sure I want to fiddle with secure boot 'til I get myself backed up, updated MR v7 to v8 including Rescue Media.
If/as required, deal with my MSFT account for my Retail Win10.
I'm taking a break (off to put some netting over our persimmon tree suffering from squirrel predations) before tackling this further.
Meanwhile, I'd be honored to have your advice on the above, but I do realize it is now off-hours on the weekend.