I am not sure he resigns.
Kamala may be allowed to take over if she agrees not to run in 2024. Even if she runs, she might face primary challenges and will lose because she is unlikeable.
I think Kamala will agree to not run in 2024 if they make her the “First Black Woman President” even if it’s only for 2 years. Then they will bring in Newsome to run for President in 2024.