Differences between /init and /sbin/init

In Linux boot order, the kernel will execute /sbin/init, however, I can see another file /init existing in the file system on my linux (CentOS 8 WSL2, Ubuntu 20 WSL2).

They are different binaries:

$ diff /init /sbin/init
Binary files /init and /sbin/init differ

What are the differences between /sbin/init and /init?

/usr/sbin/init or /sbin/init is the executable starting the SysV initialization system. For compatibility reason, when systemd is installed, it's an alias to an executable of the systemd world.

The executable /init is unusual, in a Linux system. I suggest to investigate the reasons why it's present. It could be the part of a malware.