I had the exact issue yesterday with my IPad Pro 12.9. The only way I found to fix it was to force erase with “find my” using my iPhone. Then when you re set it up do not restore using an iCloud back up, restore it (manually restore apps etc), as when I used a back up (I tried 2 different back ups a week apart) I had the same issue! Took me 3 hours to sort, good thing all my stuff is on ICloud or one drive

Note I also tried to restore using ITunes, but on 3 difference devices (2018 XPS 15, 2020 XPS 13 and a desktop) I could not see the connected IPad in iTunes or device manager (tried factory cable and 3rd party cables)