AC works great until I slow down, then it's like someone turned on the heater

Genuinely confused by this one and hoping someone here has more brainpower than me on the subject. My Compass has been doing this thing for about a month now where the AC is ice cold while I'm actually driving, like proper freezing, but the second I slow down for a roundabout or park up to wait for someone it's like the air turns to breath. It's not fully hot, just that annoying muggy warm that makes you question if the AC is even on. I topped up the refrigerant thinking that was it, no change. Cleaned the cabin filter, still nothing. I'm starting to suspect it's something electrical or a fan that only kicks in at speed but I honestly don't know enough to start pulling things apart. Found some Useful tips for diagnosing a Jeep AC that cools only on the move while googling around and it pointed at a few things I hadn't considered, like the condenser not getting enough airflow when stationary. Curious if anyone here has actually fixed this themselves and how much of a headache it was, or whether I should just hand it over to a workshop before I make it worse.