I think 2 millions so far is a good estimate based on the steam spy and a few more from GOG and Stadia.
5 millions is probably the estimate Larian has for the final release including console sales as well.
But depends on how appealing the final game will be. If it gets RPG of the year and some good reception from the media it may reach ~7-8 millions. I would expect it to sell more than DOS2 given it is more appealing due to graphics/cutscenes...
