In CA is recording of HOA board meetings legal if the board doesn't approve it?

If the board meeting is an open meeting -- your governing documents will define this -- and is thus, a 'public meeting', apparently the California Digital Law applies.

You can read how it applies to public meetings, below.

As an owner, you may be able to make the case that if your recording does not disrupt the meeting, it is unreasonable that your recording of it be denied.