From a quick search of the community, it looks like @Sam_Denton figured it out (with Tasker) and @Daniel_Westergren was researching it - I wonder if either of them have insights?
Have you tried opening an app and then viewing the device data directly (eg. via REST API or through TAustin’s API Browser) to see which properties change? Maybe that would give you some insights into what the ID would be for the particular app you had open.
Edit: It looks like someone else figured out at least a handful of App IDs. And it looks like you just need the one parameter, so you might need to flip the ‘advanced’ toggle on in the Device Command block and remove the second argument: