Thank you!
OK, assuming you tried to boot 5.1.0 just before generating that file, we are a bit out of luck: there is nothing in the journal from the attempt to boot 5.1.0, which means the boot is failing really early.
In the GRUB menu, highlight the 5.1.0 option and press e to edit the boot commands. You will see something like this:
Please take a photo. Then use the arrow keys and delete key to remove the words splash and quiet from the linux line:
Now press F10 to boot. With luck we will see more information about the failure…