This is like keeping a water balloon in your back pocket to keep you dry if it rains.
It sounds like you never used it, but be careful: uninstalling Grub Customizer does not undo the damage it has caused. Further intervention is needed, see here: [FAQ] Why you should NOT use grub-customizer
I think it is not accurate to implicate yay in this mess. If this thread has revealed anything, it is that your system has been recklessly misconfigured in multiple ways. With so many bootloaders and conflicting initramfs generation methods in use, it’s no wonder an issue has finally been encountered.