Okay, many of Newsom's vetoes are complete BS, but I think this article really buries the lead:

The proposal by itself would not have been able to take full effect because lawmakers blocked another bill to create a reparations agency that would have reviewed claims.

“I thank the author for his commitment to redressing past racial injustices,” Newsom said in a statement. “However, this bill tasks a nonexistent state agency to carry out its various provisions and requirements, making it impossible to implement.”

I mean... If you have two co-dependent bills, one where people can make claims and one where you create an agency that reviews those claims, I feel like you kind of have to veto one if the other fails. If the bill fails to establish the agency to review the claims, then how do claims get processed? Have you just created a bill that allows the people you've wronged to send their complaints into a black hole? Here's hoping this gets pushed back through at some point but either with both bills intact or combined into the same piece of legislation.