That's correct, only for grants that were made while I was living in California. Any subsequent grants I receive in my new home state are not subject to California state taxes.
Can attest to this. I moved away from California in 2021 and continued to work for my employer. I pay taxes on RSUs that were granted in California as they vest in both California and my new home state. My state (and I expect most others) has a tax credit for taxes paid in both states.
If anyone finds themselves in this situation, I would highly recommend hiring a tax advisor who can help you navigate this.