I've looked into this one a bit too. The one main thing I'm missing there, is the ability to extend it with custom views. One thing Schedule-X does, which isn't documented yet, is to allow the implementer to only use the calendar header, and then implement the "view" part completely on their own. In that case Schedule-X just provides a control center type of core, with a bunch of utility APIs; basically a framework/DIY calendar.

Also I wanted to lean more towards the Material Design 3 specification.