I subscribe to The Apiarist. I find him enlightening and humorous. It doesn't matter to me that he is in Scotland.
This was the blog I got this week.
https://theapiarist.org/broodless/
The big takeaway is that by monitoring where the crumbs are falling onto the bottom board and how widely they are spread out, you can tell the size of the cluster and when the colony is likely broodless. You keep cleaning off the bottom board and monitoring till there's virtually nothing dropping.
I'm not sure they are ever completely broodless in our climate.