Haha, creepy fun looking. When I saw it was free on steam I downloaded it, but I haven’t played it yet.
But the file structure is very unique with this game. It runs a launcher with Unity Engine, but switches to Unreal 4 Engine when you select Chapter 1. This explains why vorpX closes when you select the chapter, as a totally different exe boots up that vorpX is not expecting.
Instead you should start the game from the directory folder, not the launcher on steam. Run the Poppy_Playtime-Win64-Shipping.exe from: C:\SteamLibrary\steamapps\common\Poppy Playtime\WindowsNoEditor\Poppy_Playtime\Binaries\Win64
If you want any 3D effect, you will need to create or download a profile for this game, that is assigned to Poppy_Playtime-Win64-Shipping.exe. Or if you just want it flat, you can let vorpX auto attach when the game starts.
I see someone has already posted a profile on the cloud you could try, although it claims the 3D effect is very subtle.