Remove “Windows” Entry from Mac Boot Loader

Here, I assume the flash drive is the only external drive plugged into your Mac.

Use the Disk Utility to erase the flash drive. Use the options shown below.

Next, transfer the Catalina files to the flash drive.

If you do not want to erase the flash drive, then follow these steps.

1. Open the Disk Utility.
2. From the View pulldown menu on the Disk Utility main window, select Show All Devices.
3. Highlight the flash drive.
4. Note the Device. You should see diskN were N is a integer.

5. In a Terminal application window, enter the following command. Replace N with the integer from the previous step.

   sudo diskutil mount diskNs1
   

6. Note the name of the mounted volume. Here, I will assume the name was EFI. If you get a different name, make the appropriate substitution when entering the command given below.

   VOLNAME="EFI"
   

7. Enter the following commands.

   rm -rf "/Volumes/$VOLNAME/EFI/Boot"
   rm -rf "/Volumes/$VOLNAME/EFI/Microsoft"
   diskutil unmount "$VOLNAME"