California has passed a law that parodies the Texas law authorizing almost anyone to sue whoever helps someone get an abortion. California's law does that same thing to people who do anything with illegal guns. Is this a good idea?

I think that the "anyone can sue you" approach to enforcing a law is cruel and repressive, regardless of what actions are being prohibited. Using this to enforce anti-gun laws is bad for the same reason that using this to enforce anti-abortion laws is bad.