I found a solution (at least for my Windows 11 laptop).
REGEDIT
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.pdf\UserChoice <-- Delete the contents of this entry. (You can't delete the 'UserChoice' folder)
Now go into the "OpenWithList" folder above "UserChoice" & delete the contents of this folder too.
Close regedit & restart.
Try again:
Start, Settings, Apps, Default Apps, enter PDF for the file type & select Acrobat as the default.
Mine actually stayed that way & didn't force Edge on me.
Hope this helps!