Peltier cooling modules are pretty cheap nowadays, but they require too much power and need too much heat sinking to be useful in a wearable, in my opinion.
Either you become a walking solar panel or you have to carry around a pretty hefty battery for it to be useful for any significant period of time, and either option may end up weighing so much that you’ll heat up anyway from carrying all that extra weight around.
As much as I would love to have a peltier cooling vest, I don’t think it’s practical. However, if there existed a muscular exoskeleton (in the vein of power armor from Fallout or The Expanse) that could compensate for its own extra weight and bulkiness, then an active-cooling garment might actually work.
That would be pretty awesome, although I can’t imagine it would be anything more than a garage project without some way to significantly reduce the weight or have it handle some of the weight through some sort of active posture control.
But if those things can be resolved, I bet there are some juicy defense contracts waiting in the wings...
