See "equivocation, fallacy of".
You are trying to come up with definitions and chain them together and say that this must equal that because blah.....blah....blah. Let's not go there. Instead, let's try and come up with the actual differences between someone who thinks that Israel has a right to exist, compared to someone who thinks there ought to be some sort of ethnostate that is dominated by people of European descent.
One very, very, obvious difference between the two is that the Jewish state already exists. Dismantling it would result in a lot of grief for a lot of people. Moreover, it is not obvious that dismantling it would benefit anyone. Yes, I know people want it dismantled and they are sure that dismantling it would make the world a better place, but it is far from clear exactly who would be better off in any meaningful way if the state of Israel were dismantled, or if it were to lose its identity as a Jewish state.
On the other hand, the exact same thing could be said about the formation of a white ethnostate. Formation of such a state would result in a lot of grief for a lot of people, and it is not obvious that it would benefit anyone.
So on a purely practical level, there's a difference between supporting the state of Israel and supporting a white ethnostate.
On a philosophical level, I also see differences between the concepts of Zionism versus white nationalism. I don't think that any ethnic or racial discrimination makes any sense, ever, However, I can look at the Zionist movement and the eventual declaration of a Jewish state and see that despite my principled opposition to any sort of ethnostate, there is a practical reality that Jews were the targets of discrimination, and indeed of persecution and genocide. Whatever theoretical, philosophical, objection I might have to the formation of a government that enshrines any sort of ethnic or racial favoritism, I can see why, in the case of Zionism, the proponents would see it as necessary to escape a different form of favoritism that resulted in discrimination at best, and murder at worst. I don't think the formation of a Jewish state was the best possible solution to that problem, but it might have been the best available solution And given that it was the solution chosen, see the first point above.
By contrast, I look at the motives of the white nationalists, and I can't see anything remotely comparable. I can't see any need to have a state where people can pursue some sort of "white" way of life, free from persecution. Given that, I look for some other motivation, and all I can come up with is "We don't like black people."