Hi Mike! The mbr2gpt tool was new to me when @LorenDB bought it to light, but your first screenshot shows that it worked, or mostly worked. It says both the validate and conversion were successful. The error is about Windows Recovery Environment (WinRE) and there is some stuff available about that with Google... but I don't know enough about it to make recommendations.
Your Disk Management screenshot also shows you have an EFI partition on Disk 2, Partition 2... and I'm guessing that was not there before. So I'm not sure at all why it would not boot when you switched the BIOS to full UEFI mode. While in full UEFI, did you try to use the BIOS boot menu? For Windows and for Ubuntu?
Have you used GParted (or Windows tool) to confirm that the disk type was, in fact, changed from "msdos" to "gpt"? I would guess that it was changed, from the success reports in your first screenshot.
If @LorenDB's suggestion above does not fix it, I'd probably research the Google articles about reagent.xml and the steps to disable/enable the WinRE manually, as the error describes.
A wild guess... I wonder if your new EFI partition should be Disk 2, Partition 1, instead of Partition 2? I don't know if Windows is sensitive to the EFI placement on the drive, but it is pretty deep behind the large Win 10 C: partition, which I assume to be Partition 1.
Your Disk Management screenshot also shows you have an EFI partition on Disk 2, Partition 2... and I'm guessing that was not there before. So I'm not sure at all why it would not boot when you switched the BIOS to full UEFI mode. While in full UEFI, did you try to use the BIOS boot menu? For Windows and for Ubuntu?
Have you used GParted (or Windows tool) to confirm that the disk type was, in fact, changed from "msdos" to "gpt"? I would guess that it was changed, from the success reports in your first screenshot.
If @LorenDB's suggestion above does not fix it, I'd probably research the Google articles about reagent.xml and the steps to disable/enable the WinRE manually, as the error describes.
A wild guess... I wonder if your new EFI partition should be Disk 2, Partition 1, instead of Partition 2? I don't know if Windows is sensitive to the EFI placement on the drive, but it is pretty deep behind the large Win 10 C: partition, which I assume to be Partition 1.
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