/boot/efi/EFI/neon
├── BOOTX64.CSV
├── grub.cfg <--This should be used by the grubx64.efi
├── grubx64.efi
├── mmx64.efi
└── shimx64.efi
/boot/efi/EFI/ubuntu
└── grub.cfg <--Instead this is used by the grubx64.efi

I dont have any other linux destro on my laptop. And I also cleaned the efi partition before installing kde neon. So both neon and ubuntu are created by neon installer. Even tho neon has its own cfg it uses the cfg from ubuntu. Tho this is not a bug. It should be fixed to avoid any confusions.

I have tested by renaming both cfg 2 times. Only the cfg in ubuntu is used. The neon one is just for show I guess.