I (Stephen Downes) said on a recent post that “Alexandra Minhai says successful professional learning communities depend on four factors: being a safe space, validation by peers, crowdsourcing ideas, and accountability. If I had to create my own list it would be: tools that work, practical value, timely response, and whole-of-enterprise (and beyond!) scope.”
In all fairness, I should probably expand on why I think these are necessary (and possibly even sufficient) for the fostering of a professional learning community.
https://halfanhour.blogspot.com/2022/03/professional-learning-communities.html