How do Republicans win California now?

[RFayette 🇻🇦]

It would require some sort of realignment, wherein the Republican Party becomes socially moderate, liberal on immigration, and center-right on economics.

That may be enough to win California circa 1996 or even 2004, but the California of today is also quite left-wing economically due to generational replacement and demographic changes.  It will vote for the more progressive of two parties in almost any alignment of the two parties.