Where to report malware?

You can actually check the PKGBUILD · master · Packages / multilib / steam · GitLab

And see that the source is this Index of /steam/pool/steam/s/steam/

And you can check further the validity of the package …

I have seen that before, and turned out that actually was 100% false positive. Unless you also provide the ways you arrived to your conclusion …

You can have custom location for your games. Without access to see those locations you could not set them up, but that does not mean that it can write on all of those locations. I really recommend this reading:

Please consult their knowledge base, it is stated quite clear what is what