I ran into just this problem literally yesterday 😅. It turns out that many Linux distros (not sure which ones exactly but I’m on fedora and it does this) will ignore the suid bit on shell scripts because apparently they’re too easy to exploit for privilege escalation. Sure enough I tried it again with a c program instead of a shell script and the suid bit worked; I was able to write to a file I didn’t have permission for normally. I’m not totally sure exactly which kinds of executables are allowed and which aren’t; it might be binaries only.