Conversion of Legacy to UEFI Win 10

Your recovery environment was likely broken before you even started this process. What reagentc /disable is supposed to do is copy the recovery environment from wherever they were back to C:\Windows\System32\Recovery and disable the recovery environment:

Code:

C:\Windows\System32>reagentc /disable
REAGENTC.EXE: Operation Successful.


C:\Windows\System32>dir Recovery /a
 Volume in drive C has no label.
 Volume Serial Number is 4785-A2E0

 Directory of C:\Windows\System32\Recovery

07/21/2023  07:21 PM    <DIR>          .
07/21/2023  07:03 PM    <DIR>          ..
07/21/2023  07:21 PM             1,079 ReAgent.xml
09/24/2022  07:26 PM       548,296,442 Winre.wim
               2 File(s)    548,297,521 bytes
               2 Dir(s)  34,899,222,528 bytes free

C:\Windows\System32>

Then whenever you get done doing whatever it is you were doing you can run reagentc /Enable, and if no recovery partition exists or is specified, reagentc will establish a new recovery environment in C:\Recovery.

You do not have System Reserved Partitions. Your Windows partitions are marked as active and contain the boot files. It is not the normal Microsoft way, but it is not all that uncommon either.

I would recommend you delete the recovery partitions and create new system reserved partitions to hold the boot files. That may make D: drive bootable again, although it should be now.

"I would recommend you delete the recovery partitions and create new system reserved partitions to hold the boot files. That may make D: drive bootable again, although it should be now."

Thanks for the suggestions. Attached is the record of above commands. Although it states boot files have been created, still no bootable D. It is possible I jumped straight to the bcdboot command before carrying out your suggestion above but I am not sure how to delete recovery and create new system partitions as above and I am conscious that this exercise is generating a lot of effort on your part. Maybe the way out of this is to instal the previous image of NEW onto D: which should have the relevant boot files.

Did you mark the partition active (bootable) ? Transferring the boot files doesn't automatically mark the partition bootable.

I hope you didn't accidentally damage your system and made it unbootable. That's why I said it is not worth all this trouble to upgrade to Windows 11. I would just bypass compatibility check and upgrade the MBR Windows 10 installation to 11. It is much easier and it won't be any difference in performance or features.

Thanks spapakons and Megahertz. I checked in BIOS that D: was not an option to boot and the disc map showed that the boot files had not been loaded. Incidentally, I did load my system parameters when I registered but they do not appear in these posts. The mobo in question is a B450-M Maxtor and previously both SSDs were shown as bootable drives.
The paths I have been following are those suggested by NavyLCDR since that seemed the simplest way to be able to boot D: before embarking on other methods so no shooting in the dark. His posts answer your query as to why reagentc was disabled and enabled. In my opinion, a simple way of sorting this out is to reimage D: with a saved image made immediately prior to this
problem but I have been monitoring all solutions offered. I am using a Win 7 PC and leaving the troubled Win 10 PC as a test bed for your suggestions and yes it still boots into Win10 OLD so the system is not damaged. The objective of this exercise was to prepare the PC for upgrade to Win 11, not to actually do the upgrade. Hence the prime target was to convert to MBR2GPT. Using the validate command caused D: to become unbootable.

You can boot into D: drive in UEFI mode by deleting the recovery partitions and creating a small FAT32 partition, then put EFI system files in it with the BCDBOOT command. The disk does not have to be GPT in order to boot in UEFI mode.

I ask again, why all this trouble? Just bypass compatibility check and upgrade your MBR Windows 10 installation to 11 anytime. Alternatively, you can backup your data, delete all partitions and do a clean GPT Windows 11 installation when time comes. I know it is much trouble to reinstall everything, but if you don't frequently use that system most applications will be outdated anyway and you would want to install the new versions. So a clean installation where you install directly the last versions of the applications doesn't look like a bad idea.