According to one source I bumped into, most cantons have you jumping through loads of bureaucratic hoops to install it. You must consider noise and aesthetics, and some require you to state if you have a legitimate need for one.
One outcome is that the Swiss buy portable units in droves, and frankly, those suck.
NL here, so fortunately bureaucracy about whether AC’s are allowed is thankfully not as much of a thing here. My problem unfortunately is that I live in a rented house, and our heating setup is based on hot water radiators so grafting an AC onto the heaters is impossible, and I’d have to go via the landlord to get an AC installed. And since I’m hoping to move out before the decade is over, getting a proper system installed is not worth the monetary investment in my situation.
Best I can do is one of those weak-ass portable units, which only cool my place down to bearably hot.
Meanwhile, someone in my family has a proper AC, and their place has been a godsent this heat wave.