Noob question, but how do people know this is thrustworthy, since it's not from Arch / an official source?

There's a lot of voodoo in that script, i can't easily tell it's safe by reading the code.

I'd expect some reaction/solution from official Arch developers...

You could try rkhunter or unhide from the official repositories, but I haven't tested this myself and I don't know how well they work with BPF rootkits (and/or this one specifically).

All of the packages I have triaged involved the atomic-lockfile npm package, so this is something you could try:

  npm cache ls | grep atomic-lockfile