In synchronous update, every gene reads the current state and updates at the same time.
All genes update at the same time
In synchronous update, every gene reads the current state first, then all genes switch together. No gene gets to see another gene's new value early.
current state⟶next state
Read the current state, then switch
From state 00, both genes are OFF, so both turn ON next, giving 11.
00⟶11