I think I figured this out - seriously.
My old wallpaper (pre- iOS 16) somehow got linked to the 'Do Not Disturb' focus. (I don't think I did this)
When my phone would lock, it would try to turn on my old wallpaper, but since it was linked to the DND focus, it would put the phone into DND mode, which for some reason would put up the black screen - at least that is what I believe was happening. So, I decided to try and un-link the DND focus from my wallpaper.
If you long-press on your lock screen, it will bring up the various wallpapers and the assigned focus will be at the bottom of each. Where my original wallpaper used to be (the far left spot), there was the black screen, and the focus at the bottom said "Do Not Disturb". I pressed on the "Do Not Disturb", and it brought up all of the various focus modes(Do Not Disturb, Personal, Sleep, etc.). The "Do Not Disturb" was selected. I tapped on that to unselect it. Then the focus mode at the bottom just shows "Focus" - which means no focus is selected. This did it. I then locked the phone and voila! My old wallpaper is back, and it's not tied to a focus, and for now at least I don't have a black screen.
I hope this helps. Good luck!!