...it looks like it's just an Electron app, so all you should have to do is recompile the app with a slightly older build of Electron. (It seems very unlikely they actually need anything in the latest versions of Chromium; you don't need to go back very far for Mojave support.) This should be extremely doable. Maybe a little annoying if it's you first time with something like this, but manageable.Personally, at this particular moment, I’d prefer finding a way to backport the current source for Signal to compile and run in Mojave, but that is also unlikely to come to pass.