Comment # 4 on bug 1225292 from Dirk Stoecker

Still looks like a false positive to me. The reported results are all Generic
or Heuristic. Happens to a least one of my own software as well for freshly
compiled binaries as it includes a HTTP server component. But there is a slight
chance it's real.

I'd suggest
a) In VirusTotal was something like "report as false positive" in two forms if
I remember correct. Something like "I'm the author and sure it's a false
positive" and "I suspect it may be wrong". I recommend to report it as false
with the second category. They will check it then and either mark it as a
virus/trojan with a real name or flag it as false.
b) Report it to Steam: https://github.com/ValveSoftware/Proton/issues - Again
they will need more details: File names, file sizes, dates, ... The screenshot
is not enough.