I am not accustomed with Ren'Py, so I only did a quick Google Search. If someone knows more about it, feel free to give an answer.
Going from what you described about your system not having changed (I assume no settings and drivers included), the only things I found so far are these:
- The games can have different rendering, and you can launch the settings when holding down the 'Shift' key while launching the game.
- If you have an individual GPU, you can try going into the Windows Graphic Settings / your GPU Control Panel and select the corresponding Game .exe to use either the default or individual GPU.
- Did you set the games into Full Screen? I found something in a steam discussion that talks about this issue: https://steamcommunity.com/app/398980/discussions/0/496881136912317915/?l=polish
Maybe this will help you.