Just wondering. Some games are in Ren'Py, some in Unity. Which is graphically better, easier on pc-specs etc.?
It depends on what game you want to create.
Ren'Py, just like RPG Maker MV/MZ, is a tool that allows you to create a local website. As a result, the easiest things they can do is load images made externally and display them. Just like in RPG Maker, there are no limits for Ren'Py so long as you know how to write python & html & javascript.
The existing tooling for this website, in this case Ren'Py, is specifically optimized to make displaying dialogue accompanied by images as easy and quick to do as possible - to the detriment of everything else that you'd have to code yourself.
Unity is an actual game engine that renders the game in 2D or 3D, depending on what assets you use.
No engine is graphically better or better on pc specs. The best 3D results can be gotten with the Unreal Engine, which has the most advanced inbuilt 3D graphic features and is pretty darn quick in its rendering. But if you code things wastefully and mess things up, you'll kill your game's performance same as everywhere else. Performance is primarily always a question of optimization by the developer.
While the Unreal Engine can make the best 3D renders on the spot, it doesn't quite compete with the sort of highly controlled rendering of images or animations you can get from Daz3D or especially from Blender.
In other words: no Unreal Engine realtime animation will ever compare to a pregenerated Blender animation.
TLDR; your question has no good answers. It's a question that lacks the necessary basis (type of game, type of graphics, type of gameplay) that would allow a good distinction between engines. In theory, every engine can do almost everything - it's just a question of you programming it to do so. That's why engine choice is usually based on what engine suits your
particular game best because it's more optimized for that specific type of game or has plugins on sale that would aid you, and what engine you're most comfortable working in.