I don't know where to go to talk about this, but after migration, the Category Exhibition layout has been disabled for my wiki. Is this permanent?
Yes, the change is permanent. See here for an explanation.
Is there any way to re-create it using Java Script or CSS?
I don't believe so; especially not with just CSS. However, feel free to ask on Fandom Developers Wiki.
How about CSS to change the size of the images on dynamic categories?
What do you think?