I am a lamer in the knowledge of the Raspberry Pi platform, I bought myself a Raspberry Pi 4. I want to make it multibootable, but not with the help of BerryBoot or PINN, since I do not like their functionality, because, if I understand right, that in the first case, the OS images must be specially adjusted from https://berryboot.alexgoldcheidt.com/images/, and in the second case only those that are in the list. And _{I want to install several OSes and, ideally, to load them like on my PC using GRUB2 or similar way}. However, I do not know how to install GRUB2 on the micro SD correctly. The OSes I want to install are Rpi OS and Haos (Home Assistant OS, which neither BerryBoot nor Pinn is listed). There is no BIOS or UEFI on the Rpi4, I am looking for information on how it could be done.
_{There are several articles with useful information that anyway hard for my brain:}