I've tested this on a phone with Oreo and the soft pressing does work, unfortunatley I don't have a phone with Pie on to check at the mo'.
How hard are you pressing it?
I noticed at first that I pressed with a tad too much pressure and ended up taking a 30 photo burst of my keyboard.
It's hard to explain, its the smallest little touch that allows you to do it.
As soon as your finger touches the shutter button, start your swiping.
As you've already said though, it may well be a feature that has been removed with Pie.