In short: it's too early to tell.
My prediction though? At the rate the Switch is going, unless sales drop like a rock, it is on pace to sell 120-130M minimum. The PS5 has a great start, but 120-130M is not standard for consoles. In fact, only two consoles have ever broken that record with a third coming up. Also, the PS4 sold really well because it was the de facto console. All third party games ran better on it by default, plus it had killer exclusives. There was little reason to get an Xbox One (unless you enjoy Gears and Forza). Series X, however, has hardware that is at the minimum comparable, and on paper better (though real world results are showing a slight edge to PS5). If MS gets their head in the game and deliver on avowed, fable, everwild, Infinite, and Hellblade 2...I could see it eating into the market share. Instead of a 3:1 split in favor of Sony, I could see a 5:3 or, at max, a 4:3 split. If the first is true then PS5 will sell 110M with Xbox selling almost 70M. If the latter is true then PS5 will be at 100M and Series X will be at 75-80M.