This is definitely it, you beat me to it! Thank you

I second this point, a fresh install is definitely the way to go.

Good spot & thank you for the correction!

Step 1: make a backup / clone the disk

Step 2: double check the backup

Step 3: Assuming you’ve got a grub bootloader, boot into Linux Mint, use GParted or Gnome-Disk-Utility

Step 4: Identify your NTFS Windows 11 partition, the utility should show if it is mounted or not (it should not be mounted unless you added it to /etc/fstab

Step 5: resize your Linux mint partition (ext4fs), & make sure you don’t accidentally move the partition

Step 6: sudo update-grub to remove the entries for Windows 11 since it doesn’t exist anymore

More info on if you’ve got an HDD vs SSD, MBR vs GPT partitioning, or a screenshot of your partition table from either of the disk utilities in step 3 would help us help you