Maybe we should adress this. Open the Terminal and type sudo nano /etc/default/grub
and then You should get something like this:
The white Textblock is the Goal here. Navigate with Arrow Keys to it and add at the bottom the Line:
GRUB_DISABLE_OS_PROBER=false
Then it should look like this:
Then press ctrl+o to save the Change, Enter to confirm and ctrl+x to exit. Back in the normal Terminal type sudo update-grub to make affect the Change. Don't forget it! Without that it will not work.