Okay, you've asked for "other" suggestions. So feel free to ignore this - because this isn't that.
[...] Initially, I was thinking about Renpy except for two issues: As mentioned, I have no art skills and also, I would very much like for the game to have "hidden" interactions, meaning the possibility to discover stuff through experimenting with the environment.
You probably need to separate out in your head "graphics" and "engine".
Whatever engine you end up using... you're going to need some images to populate your game... Unless you go for something like Unreal or Unity... in which case, you'd need true 3D models (Not that Unity or Unreal can't do flat pictures too).
Those images might need some art skills. But the engine doesn't care if you use photorealistic images, cartoons, hand drawn art or even a doodle drawn in Microsoft Paint. They're just pictures. Where you source those pictures from is irrelevant to the engine.
- So for example. You could have a pure black screen and just text. No artwork required. Even HTML games don't get this basic... but you COULD.
- You could just grab some photo stills from porn movies staring your favorite porn actor/actress. Write a story that stitches those images together and voila... you have a game. Lots of HTML DO use this method.
- You could (as many others have done) dip your toe into Daz3D. Daz isn't really about art skills. It's about learning the technicalities of how to add lights. Where to position the camera. Where to download free/stolen assets from. But mostly, how to pose characters so the don't look like they've got a broken neck or dead eyes (preset poses help a lot as a starting point). Once you find a set of render settings that work 99% of the time for you... you're sorted.
- Finally, as has been my mission lately, I'll also mention Honey Select. Not because I've ever used it (I haven't) or even because I like it's art style (I don't hate it either)... but because it looks a simple way to create scenes with characters in - at least to my inexperienced eye.
In the classic Renpy style, everything is just a multiple-choice menu so no secrets. I realise you can make point and click interactions in Renpy but again, no art skills.
And it's that "point and click" capability that could implement the hidden interactions in RenPy.
Short version is that you take a full image and cut out an object and add that 2nd copy of that part of the picture to something called an
imagebutton:
. You can assign a 3rd copy of the the same part of the image to the definition so that
it changes color... or gets a colored halo... or something that lets you've moved the mouse over something special... Or NOT. You could make your game particularly hard by not giving the player any hint they've moved the mouse over something important. The player clicks the object and the game does something (usually jumps to a section of the code that shows a new scene).
The difficult part here isn't art... just learning how to cut out sections of an image in an image editor like Photoshop, PaintShopPro or GIMP to create layered images... more specifically images with largely transparent areas (transparent areas are ignored by
imagebutton:
. That's a technical skill... not art. (at least in my opinion).
If you can pick up the basics of cut/paste in something like Photoshop and get a single
imagebutton:
working... You're 80% the way there to implementing your "hidden" interactions in RenPy. If you can do it once... you can do it 100 times again.
All of which is my way of saying that maybe you don't need to be an artist and maybe RenPy is the simplest solution for what you're trying to achieve. That said, I've never tried programming any of the other engines mentioned in this thread... so I am somewhat biased.