Critique: This experience is delightful! I know the physics thing was an happy accident but I actually quite enjoyed the bit of environmental storytelling. I felt like a witch that conjured something that was a bit out of my league and I was cleaning up the aftermath :). I really enjoyed the color palette, playfulness, cute room layout, and little witchy discoveries to make. It reminds me of a Silver Ravenwolf book come a life. Playing this reminded me how little there are good femme witchy games out there about empowerment and playing with magick. I really like the theme :) I think to push this further I would add interactions that occur when two objects meet, little animations here and there, music/ambient noise, and sounds.
Technical: So I think what's pushing all your books around are the collision boxes :) Here's a quick video that shows how to create custom collisions in 3D software
You can also read more about it in the "collision" section of this page: https://docs.unrealengine.com/en-US/Engine/Content/FBX/StaticMeshes/index.html
and lastly if you have uncomplicated meshes like bookshelves and tables you can add your own collision in Unreal really quickly (this is my favorite method lol):
Recommended (witchy, femme, cute, narrative):