Is that actually true? I've met very few project managers who know any discipline other than project management with anything I would call depth. I can't even imagine talking to a PM about any serious technical question anymore. Their answers in the past have always been a unique type of unhelpfully vague but hard to argue with which puts all the effort back on you, but not in a way which adds anything to solving the problem.

Things like "what's best practice" when I've just exhaustively explained how we're in the precise corner case to which the normal best practice doesn't apply are, for me, the hallmark of PM ideas. Deep technical insight or domain knowledge are not.

Yeah, I have found a few PM's who were "used to be technical". To be honest I found it a bit frustrating at times as they would think they knew enough to make (some of the) technical decisions, when I felt that I should actually be making those decisions as was the one actually getting my hands dirty with the code. Plus I had more experience as a developer than them, as they had transitioned to PM and hadn't actually been building stuff for a while.