It does, I’ve two games on the MS store that appear to still work.
However, there are limitations.
No support for subscriptions (if I recall) and it only supports public audiences, not private.
There might be other limitations, but I’m not aware of them.
Unity have hinted at changes on the IAP\UWP front, but haven’t clarified what they are. It could be dropping support for it or improving (as it’s using an old Windows API and hasn’t been updated in a long time)