>>106399790
SuperSu was just an app for installing, updating and managing su into the /system partition, back when it was ext4 and could be remounted rw. At least devices I dealt with, it was usually installed by either unlocking the bootloader or using an exploit to replace the recovery with a custom one like TWRP and then using that to unpack a zip into your /system partition to add the su binary.
Today /system is erofs which is inherently read-only and basically like squashfs, so you can't add or change anything in it short of rebuilding the whole ROM. So instead there's Magisk which typically loads as part of the initramfs and mounts overlays on top of various parts of the filesystem. There are some "hide" modules for it, but it all runs as user processes which makes it harder to hide. KernelSu is a newer option that does very similar things but stuffs more of it inside a set of kernel patches since stuff running inside the kernel is harder for user processes to discover.
