Yes, it's possible to create Lake Congo, "mathematically" speaking.
But why ?
Lake Congo was supposed to be a thing where you put all the water that no longer belongs to the now drained Mediterranean sea. The existence of this lake means that any resource (and there are a lot of them in this part of Africa) here would now be underwater, which is just an idiotic mistake. Loads of people would be there, which being a humanitarian disaster aside, would be an... inconvenience for the Colonial government in Zentralafrika. And a now unnnecessary one, given that there is no more Atlantropa.
They proved they could, but they never said why they should without the aforementioned Atlantropa.
Maybe because Nazis bad ?
And lol at TNO being realistic. TNO was meant to be the pretty unrealistic, even if not Red Flood levels of so. But now with updates like these, TNO has become this unrealistic mod, with the additional touch of deluding itself into thinking its realistic. TNO could have embraced a grimdark setting, and set things... semi-realistic, not aiming for total realism, and not aiming for excessively insane concepts. But no, they have to be the 14th "realistic" axis victory scenario, even though TWR is right there.