This is for RubyMine 2020.1.4 on macOS 10.12.6 (Sierra). I don't think I can upgrade because I'm on an older MacBook and can't upgrade to a newer OS, and when I tried a recent RubyMine build I couldn't launch it because my system is too old.
But I think there should be a Problems Tool Window somewhere? I mean I was using RubyMine 7 years ago, and am pretty sure there was a Problems Tool then.
Weird… I have GoLand as well, and it has a Problems tool window.