How the heck do I get gamescope working with Heroic Games Launcher?

This is one is very confusing, which probably speaks to the current UI in Heroic. I just want to say, run this game in gamescope, so I can use HDR.

I have the latest version of Heroic, installed via Flatpak as the devs recommend. If I go to configure the game in the UI it has an entire settings page dedicated to Gamescope but nothing that says "enable gamescope".

Anyone get this working?