I hang around at a lot of different Linux forums and I have heard many bad things about grub customizer. Here is a current thread, but for at least the last few years grub customizer has had a bad reputation. My personal experience was just so-so.
Same here, although wasn't trying to do the same as the OP. Was using to fix Grub when all I had to do was use the bootable Live distro & run a couple of commands.
The Grub Customizer, even though I followed instruction, left me with two, maybe three Linux entries, although only one distro was installed & wiped out Recovery, which most distros picks up just fine. Can reload Windows via the Grub menu & have done so.
Although for some who knows how to use the tool well, may have better success than I did a couple of years back. I still prefer using the Live installer of the distro, a fast Google search can get one out of any jam. It did what I couldn't with Windows tools in getting Ubuntu out of the system partition. My guess would be that it would do the same for the Apple folder, as well as delete no longer used entries. Unfortunately, I didn't bookmark the page, if I had would had included with the instruction in my last post. It's all a mater of identifying the OS's no longer installed & remove, then clean up the system partition, reboot & everything is magically fixed, no harm done to the filesystem. Here's a little of what the article spoke of, although a lot broader than what I was looking for a couple of days ago.