You might look into taking apart your door and trying to clean out the junk in your windows, and maybe find a clean window from a wrecker.
First I'd probably need to check to make sure you're using a proper polisher like a Rupes, or a G110, or a Torqx. A 3" backing plate. A quality polishing compound product like Ceriglass and not some alibaba cerium oxide, and the Carpro 3" rayon polishing pads. I say this because some of you guys seem ready to jump into a detail with some garbage you picked up from ebay or harbor freight, frightening. If you just ordered a bucket of brown cerium oxide powder, please stop right there.
I would be very careful with Ceriglass on these cars. Ceriglass is some nasty polishing stuff, very messy and slings everywhere (you'll want to tape off and cover everything) and rayon pads are very rough.. and Subaru BRZ / modern car glass is very soft.
I've used Carpro's Ceriglass and Carpro Ryon glass polishing pads only on the front windshield of my older 90's Toyota Camry. After a few passes with my DA buffer it fixed a lot of lateral or cobweb scratches that were caused by sand debris caught between the wiper and the glass. It would be important to note though, that modern car glass is softer than 90's car glass and so you might be careful to not work it too aggressively, but enough to break down the abrasive material.