The Biden plan was not right. The Biden plan was stupid. It's the sort of thing someone who thinks they're an expert because they read a Wikipedia article would come up with.
3 words: Baghdad, mixed city.
What is your proposition? The Shia and Sunni hate each other, and the PKK is relocating it's forces to Northern Iraq.
There really isn't a good solution but the Biden plan would actually make things worse.
Again, what do you do about mixed cities? Who gets Baghdad? Who gets Kirkuk?
If it looked like a split was likely, each side would up the ante in terms of ethnic cleansing to make sure they got the disputed areas.