Hmm... I tried adding --ignore-gpu-blacklist to the package.json and package-preview.json files you linked, and it didn't work, still getting software rendering.
What does work, however, is making a shortcut to the exported exe file, right clicking it, and editing the properties so that the target is:
Then running the shortcut, I get 60 fps again. I tried modifying the shortcut to use --disable-software-rasterizer, but it still didn't work. Kinda odd that --ignore-gpu-blacklist doesn't work in the package file when it works in the shortcut.