Pre '90 buses titled and registered in California are subject to these regulations. If registered as motorhome/housecar/RV, a bus conversion still has to register in the CARB database, pay the 30 annual fee for 2023 and 2024, then submit to smoke/accelerator testing ONCE per year, starting next year as the start has been delayed.
RV registered outside California can travel through the state without regard to the CTC regulations.
The specifics are better provided via the CARB CTC website.
Practically speaking, you could wait until next year and then see what happens when you receive your registration renewal that might indicate a hold from CARB. CARB has stated it is asking DMV for vehicles that fall under the regulation. It's unknown their internal process for filtering the target vehicles, then notifying DMV which ones to place holds on for noncompliance.
Personally, I registered and paid the 2023 and 2024 fees, now just wait until next year. My bus passes the opacity test with flying colors so I good to go when this all hits.