AppImage is a lot better than Flatpak because it isn't a walking security nightmare (http://flatkill.org).
But yeah, I got a build working with the PR. I'm not on my computer right now, but it's a pinned PR in the GitHub issues for the WebCord project. You go to the fork with the branch, you run a couple of quick npm commands and then you can do a build.
I did have to remove a few of the package makers because they'd set it up to do a .deb build, and I haven't used apt in years. I vaguely think they had a Flatpak or a Snapcraft package maker in there too, but I don't use those.
You run the make and package commands which you can find in the package.json file, then it outputs a built application for you.