Linux Boot Trouble: "Gave up waiting for root file system"

I recently ran into the error above while trying to start up my dual-boot Lenovo laptop (Kubuntu + Windows 11). These are the steps I took to fix it.

1. Starting with this SO post, I did the following:

   1. Start up the laptop with a bootable drive. I used a popos one that I happened to have on hand

   2. Open a terminal and run sudo blkid, which gave the output below:

      

   3. Ran sudo mount /dev/sda3 /mnt and got the following error: mount: /mnt: wrong fs type, bad option, bad superblock on /dev/sda3, missing codepage or helper program, or other error.

2. Ran sudo file -s /dev/sda3 to check the filesystem type. Output was data, suggesting this was likely not the right partition. No other partition seemed to be the one I was looking for.

3. Went to BIOS to check various settings

   1. UEFI/Legacy Boot: UEFI only

4. Went to Lenovo boot menu and selected “Ubuntu” → was able to start up (?!)

5. Ran the following to reinstall GRUB Bootloader:

    sudo grub-install
    sudo update-grub
   

6. Ran cat /etc/fstab to make sure things looked right: ✅

    ~ 
    ➜ cat /etc/fstab
    # /etc/fstab: static file system information.
    #
    # Use 'blkid' to print the universally unique identifier for a device; this may
    # be used with UUID= as a more robust way to name devices that works even if
    # disks are added and removed. See fstab(5).
    #
    # <file system>             <mount point>  <type>  <options>  <dump>  <pass>
    UUID=2799-345B                            /boot/efi      vfat    defaults   0 2
    UUID=29b53720-ce06-4cc4-8465-fd9ac544f52d swap           swap    defaults   0 0
    UUID=421b7727-75b0-4825-a330-c620b04dcb64 /              ext4    defaults   0 1
    /swapfile                                 swap           swap    defaults   0 0
    tmpfs                                     /tmp           tmpfs   defaults,noatime,mode=1777 0 0
    ~ 
    ➜
   

7. Saved a backup of my fstab in case this happens again:

    sudo cp /etc/fstab /etc/fstab.backup
   

8. Rebooted the laptop to see if the fix held: ✅

9. Removed several old popos entries in the laptop’s boot order. Not clear if those had anything to do with this, but can’t hurt to remove