Since there are many minds, therefore there must be many worlds (produced by those minds).
How those worlds look depend on our individual mental patterns.
Consciousness-Only Buddhism can be described as “objective idealism” because it teaches that there is one external world, which is perceived differently by each mind.
However, Hua-yan Buddhism is “subjective idealism” because it teaches that each world is actually different, inasmuch as they are the creations of different minds.