Basically I have a dual boot with Zorin OS and windows 10
Both were working fine until I wanted to add more space from windows to Zorin OS.
I shrunk the drive and created 100gb unallocated space in windows and booted up live USB to add this space onto the Zorin OS partition using gparted. However gparted wouldn't let me do it.
So I tried rebooting into Zorin OS to check everything was still ok and it wasn't, I was stuck at this grub 2.04 text screen. I tried booting back into live USB to run boot repair but recommended repair option isn't there.
However the Zorin partition is still displayed in gparted and I can still boot into windows fine using boot selection in bios.
Oof... they need to be adjacent in order to expand Zorin into the freespace - and they are.
But Zorin OS is reading as Unknown FS...
Not good... Have you tried running fsck on the drive?
Let's assume for the moment that there is Drive Failure...
The System will move data to occupy new space if it outgrows its assigned space, avoiding bad sectors or blocks. This is normal with ext4 journaling file system.
But if partitioning occurs during drive failure; then the shuffling of many blocks can cause data to be placed on a bad sector or block. It Brings into the spotlight the drive failure that had been going on for a while. I am not saying that this is the case, but it makes sense and seems a probable explanation. It's not something you did or could have predicted, if so.
You might run a S.M.A.R.T. test on the drive to check.
In the meantime:
Create a superblock backup
mke2fs -n /dev/sda5
It will list stored superblock backups. Pick the First Number (For example 12345 and replace the 12345 below with the actual number you see in the terminal window) and use it to try running fsck using the backup you just made:
Using your Live Media... are you able to access your personal files and make back ups?
Honestly, At this point, if this was me, I would back up - check drive integrity and if it is reasonably usable, perform a reinstallation. The unknown partition and Existing Zorin partitions can be deleted and reclaim the space both creates.