Just finished attending a weekly book club (Fundamentals of Software Architecture by Mark Richards and Neal Ford -- great book for mid and senior developers, as well as new architects).

2 chapters weekly worked well because the chapters were short, and were mostly brief overviews that discussed the pros and cons. (Also we had a ton of experience in the room, so that helped guide the discussion.)

If the chapters were dense I would have longer gaps between meetings to allow people more time to read and reflect.

In person I did biweekly (fortnightly) and that seemed like a fair frequency. Virtually though there's a new discussion started every week.