I might recommend something Arch-based that's opinionated and feature-complete, like Manjaro or Garuda, but I'd recommend pure Arch to the same people who would equally enjoy NixOS.
I'd recommend something that guesses how to install grub onto your system correctly for beginners, and let them figure this stuff out when they're used to basic Linux usage TBH
I had many problems with installing grub in a dual boot configuration, so much so that I moved to systemd-boot and never had problems after. I don't know why, but it's config file approach felt more intuitive.
I'm actually not sure why GRUB is such a popular boot loader that comes packaged with so many distros. Maybe GRUB does something more complex than just bootloading, but I don't know if most users would care...