This entire list: https://www.shellcheck.net/wiki/

How is any of that a subtle difference between platforms?

The tools you will call from your bash script differ in subtle ways between Linux, macOS, MinGW.

One good example is `uuidgen`

>uuidgen

That's neither a standard CLI utility nor a bash builtin.

Technically maybe, I don't know. But in practice, your bash will use tools like this and break if they are different / missing on a future build host.

If using a programming language with locked-down package dependencies, then all you need is the compiler/interpreter and your script will work.