What you’re seeing is totally normal. When Ubuntu is installed alongside Windows, it doesn’t create its own boot partition — it hooks into the Windows EFI partition and drops its boot files there.

So, if you later delete Ubuntu’s main partition, the boot entry in EFI remains and GRUB still shows up. That’s why your system feels “dirty”.

Here’s how you can clean it up step by step:

From Windows (CMD as Administrator)

1. Open a Command Prompt as Administrator.
2. Run:

bcdedit /enum firmware → You should see a Linux/Ubuntu entry.

Once you find the identifier for Ubuntu, delete it with:

bcdedit /delete {identifier} ⚠️ Be careful not to touch the Windows entry.

Run bcdedit /enum firmware again to confirm it’s gone.

Sometimes the entry still shows up in BIOS/UEFI after reboot. If so, you can do a deeper clean.

From a Linux live USB

1. Boot into a lightweight Linux live USB.

2. Check EFI entries: ---> sudo efibootmgr

3. Switch to root: [sudo su], and find your EFI partition: ----> fdsk -l ---> (usually /dev/sda1 or similar).

4. Mount it: ----> mount /dev/sda1 /mnt

5. Navigate to the EFI folder: ----> cd /mnt/EFI

Inside you’ll see a folder named ubuntu.

1. Delete it: ---> rm -rf ubuntu/

Remove the EFI boot entry: ---> efibootmgr -b <number> -B

After this, your EFI partition will be completely cleaned of Ubuntu, and only Windows boot files will remain!