2019 ST with around 40K miles.
We get no heat at all unless you are above 2000 RPMs. Then it works as normal.
I did see a code using Forscan about a coolant pump- but it never turned on the light, it's just stored. I will pull it again and get the number.
I also tried the method to recalibate the HVAC system and everything didi what it was supposed to in that process, but nothing changed.
I'm about to take it to the dealer, but I thought I'd make a post here first to see if the hive mind has knowledge.