@Olo As long as it’s kept to fantasy, I try not to judge preferences like “all-men-shrink-because-reasons.” I’ve explored the opposite concept myself (which turned out to be some of my darkest stories).
I’ve always liked the idea of everyone shrinking but one or two people. It’d be interesting to see how the normal-sized person reacts. As a savior? A destroyer? You can create dozens of different stories just from that one concept.