Not necessarily a solution to your issue, but the "easy build path" in the README worked just fine for me on Fedora 31. Install vagrant and its qemu backend (assuming you have virtualisation available) from dnf and you're good to go.
Yeah I'd strongly recommend using the Vagrant-based build path that @Newbytee mentioned. Setting up a system to build Proton is not easy, and the Vagrant stuff will take care of that for you.
Nothing extracted yet.
I followed this guide: https://github.com/ValveSoftware/Proton/wiki/Build-instructions-(Fedora)
my environment:
proton version 5.0-5 with commit 22f40122788d5f65389f59144705309ce9d6d403
docker images exist:
I followed all the commands up until the "Build" section that says
Now it's time to build Proton itselfthe
makecommand failed:i noticed that i didnt install steam, i did that via dnf from the 3rd party repos, but that didnt change the situation