I've found that many people are really, really averse to the perception that they're "bothering" their manager, no matter how often it is emphasized that ad-hoc

I've found that many people are really, really averse to the perception that they're "bothering" their manager, no matter how often it is emphasized that ad-hoc conversations about things that are important to the teams' members are part of the manager's job and despite however much effort the manager puts in to genuinely welcoming these ad-hoc conversations when they happen. Regularly scheduled 1:1s are a great backstop for this kind of thing, and let people feel confident and prepared for conversations with their management. If neither party has anything to say, its true the meeting can become a dumb status update - but if neither party has something to say, that implies the time since the last 1:1 saw no growth, no challenges, nothing of note at all to bring up... and this is probably a red flag on its own. I'm perfectly willing to reduce frequency of 1:1s with very senior and self-sufficient members of my teams, but even once a month is valuable.