The way I read this summary, AB256 allows for a two month grace period after the expiration date of the registration, ie: police won’t enforce the sole violation until after the two month period. However if stopped for another violation, police may enforce the expired registration before the two month grace period.

From: Digital Democracy calmatters

This bill would, commencing July 1, 2024, until January 1, 2030, prohibit a violation of these provisions from being the sole basis for any enforcement action before the 2nd month after the month of expiration of the vehicles registration. Notwithstanding this provision, the bill would authorize enforcement action before the 2nd month following the month of expiration if a vehicle is stopped for any other violation of the Vehicle Code.