I have used several cheap wireless chargers with this phone and they all work very well even with the case on. No heating issues even when I didn't have AC in my apartment and it was like 82F. So it's definitely an issue with the polestar charger. Either a defective unit, or something is wrong with the software and how it's trying to charge the phones.I would say most people that report on their wireless charging experience on any phone report a similar problem, including me (though I have an iPhone 12 Pro). But some people, seemingly a small minority, say it works fine.
I don't know what the issue is. I'm considering contacting Polestar, but I wish I had another wireless charger to test with first.