hard disk – Is it safe to delete an EFI partition that is likely a residual one left behind by Ubuntu

You could mount the EFI system partition, and double-check that it only has an EFI/Ubuntu directory, and no EFI/Microsoft directory.

You could do this by booting a Ubuntu installer in “Try Ubuntu” mode, e.g. using the Disks app in Ubuntu.

Or, you could try using Windows. For example, you might be able to mount the EFI partition to a Windows drive letter, using the Disk Management app you have screenshot in your question. See Change a drive letter.

Finally, if you use fdisk on the Ubuntu command line, you could:

1. Write down the number, start sector, end sector, and type of the partition.
2. Delete the partition.
3. Reboot into Windows.
4. If Windows breaks, you can use fdisk to re-create the deleted partition. All the partition data will still be there. (Unless you created a new partition to overwrite it!)