I may have brought this up/submitted as a feature request before, but it came up again and I wanted to make sure I passed it along! We could really use the ability to have a *private boards/private board groups* within a Collection. Our use case is that there is documentation that only managers should have access to - and our current solution was to create a Managers-specific Collection, but we've gotten feedback that having two Collections to check is too much mental overhead.
We also don't want to just make all of these cards private and in our all-team Collection, because adding individuals to 10+ cards every time a new manager is hired is not scaleable and also prone to inaccuracy due to it's manual nature. (Card privacy settings by user group
could work in this case, maybe! So, there's another feature request for ya!

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Let me know if there is another solution that I'm not thinking of!