Installed Windows 11 on a separate partition, Windows 10 now inaccessible

I recently upgraded to Windows 11 while upgrading my self-built PC's hardware. It turned into almost a complete gut job except for the hard drives. I added an M.2 SSD and planned to install Windows 11 on that and dual boot my Windows 10 setup for a softer transition. Unfortunately, while Windows 11 works just fine, my dual boot ideal has failed and I no longer have access to my Windows 10 setup. The hard drives are all good, they are there and files are accessible, but I cannot boot into Windows 10. I honestly don't care about keeping Windows 10, but I wanted to have access to all of my programs and gradually build them up on the other partition.

From my research I've learned that UEFI / GPT are very different from BIOS / MBR. I still don't know much about that other than they don't play nice. On the advice of one article I used Partition Assistant to convert my Windows 10 drive from MBR to GPT. That was successful in it's conversion, but failed to make it a dual boot option.

My question for you all is: 1) Is there a way to turn this around and make it a working dual boot situation, or am I too far down the rabbit hole to go back, and 2) Since I don't really care about Windows 10, is there a way to access the programs I have installed on my Windows 10 partition from Windows 11, since all the data is there.

Much appreciated,