How do I know which grub version is used and how to configure it?

[Ralf Mardorf]

PPS: If you have installed GRUB via Ubuntu 20.04 or newer Ubuntu
flavors, then GRUB legacy is not an issue for you, because GRUB 2 is
simply the newer version of GRUB legacy. GRUB legacy has been out of
date for ages, discontinued. I don't have all the differences at my
fingertips, just like I don't have all the differences between GTK2 and
GTK4 at my fingertips.
Anyway, you can install a different bootloader in each partition, which
one you then use depends primarily on the BIOS/UEFI settings and can
also lead to chainloading.