Israel already belongs to the Jews spiritually, from Deuteronomy

Genesis 26 (V4-5) : And I will multiply your seed as the stars of heaven, and I will give your seed all these lands; and by your seed all the nations of the earth shall be blessed; because Abraham listened to My voice and kept My charge, My commandments, My statutes, and My laws.”

Here, God promises Abraham 3 things,
(1) He will multiply his seed as the stars of heaven
(2) He will give his seed all these lands
(3) He will bless the nations of the earth by those seeds

Deuteronomy makes it clear this prophesy has been fulfilled at the time of Moses. He says:

Deuteronomy 1 (V10): Yahweh your God has multiplied you, and behold, you are this day like the stars of heaven in number.

Here, Moses clearly goes back to Genesis's narrative, to show this prophesy has been sealed. This is the main evidence, and the clearest one. There are also more verses that point to this fact, like Jeremiah.

Jeremiah 4 (V1-2): “If you will return, O Israel,” declares Yahweh, “Then you should return to Me. And if you will put away your detested things from My presence And will not waver And you will swear, ‘As Yahweh lives,’ In truth, in justice, and in righteousness; Then the nations will be blessed in Him, And in Him they will boast.”

Notice the model us causality between Israel and all the nations.

Israel repenting --> Blessing the nations (all people on earth)

This is the exact same model as in God's promise to Abraham, where he says the nations will be blessed thru his seed.

The conclusion is clear: Israel is owned by the Israelites by spirituality, even without proper military conquest or physical ownership.

"But how do we know the physical conquest wasn't already done?"
Because when Moses verifies the prophesy is over spiritually, he sends some Israelites to go many places, and from then one conquers them.

Deut 1 (V7-8): Turn and set out, and go to the hill country of the Amorites, and to all their neighbors in the Arabah, in the hill country and in the Shephelah and in the Negev and by the seacoast, the land of the Canaanites, and Lebanon, as far as the great river, the river Euphrates. See, I have given over the land before you; go in and possess the land which Yahweh swore to give to your fathers, to Abraham, to Isaac, and to Jacob, to them and to their seed after them.’