GRUB rescue prompt means that the bootloader was unable to find the GRUB configuration files necessary to load the operating system.
You might have tried the steps to manually find the filesystem.
For example, like this
grub rescue> set root=(hd0,msdos5)
grub rescue> set prefix=(hd0,msdos5)/boot/grub
grub rescue> insmod normal
grub rescue> normal
unknown filesystem error message after running the command insmod normal in the GRUB command-line interface could indicate that GRUB is unable to find the filesystem containing the GRUB configuration files as I said before.
This issue could be fixed using boot-repair tool available in the Ubuntu PPA
For this you need to create a Ubuntu bootable CD/USB. Earlier boot-repair couldn't be installed in 22.04 or 22.10. It however installs in Ubuntu 23.04. So I recommend a fresh Bootable drive of Ubuntu 23.04.
To create and boot into a live USB follow the steps 1-3 from https://phoenixnap.com/kb/install-ubuntu-20-04
After booting into the drive click on Try Ubuntu. Open a Terminal and run the following commands
sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair
After installing boot-repair open it from terminal using boot-repair or open it from activities panel on top left.
Click on Recommended Repair and it would fix most problems including yours.
After that remove the bootable drive and try to boot the system again.
