I guess I need clarification. Your missing D: drive that runs Win 10 must be on a different physical hard drive than your boot C: drive, that runs Win 11. Right? In other words, your missing D: drive is your old drive C, that was assigned a different drive letter by Win 11, or by you when you mapped the drive to D:. Right? Can you still boot from the old hard drive? If so, is all your data visible?
That's all in an upstairs office. I'm downstairs in the evening and to avoid having to go upstairs for whatever I need computer-wise--I'm 79--I work on my laptop.
BTW, this afternoon, I did some messing with stuff and got to where now the laptop sees the desktop as well as the D: drive, but I still cannot get to the folders there. In other words, I've made a little progress.