What is unit.sh? and is it safe?

With macOS Ventura, the Background Apps settings unfortunately shows incorrect information. Sometimes the "apps" listed will be some sort of lower level utility or script. If this is where you are seeing this appear, then just ignore it since the Background Apps feature of the Ventura System Settings is currently broken unless you are having some sort of system issue you are trying to resolve. There is no way to know what items appearing here belong to any particular app.

If you are seeing this somewhere else, then please clarify exactly where it is appearing.

There is no way to know if a file is safe or malicious from only the file name. The .sh file type suggests it is probably a shell script, which is simply a (human readable) list of commands to be executed on a computer, usually by the Bash command shell. These are usually a part of the computer's software. However, it would also be possible for a Bad Guy to give a malicious file the same name simply to hide it.