new version of system-tools-backends has been released for a long long time. but the portage only have stb-1.x version. so here is the new version ebuild Reproducible: Always
Created attachment 124326 [details] ebuild of system-tools-backends-2.2.1
It's in the overlay, and has been for quite a while. However, it doesn't work on gentoo. Many of the things you're supposed to be able to do cause various crashes in various vital services, rendering your system unsuable. This is why we haven't pushed it into portage. Until someone has the time to make it actually work on gentoo, we won't be adding it.
Reopening to fix resolution.
This was applied to the tree. Thanks for reporting.