The phrase "almost impossible to sort" is correct and usable in written English.
You can use it when describing a situation or task that is very difficult to organize or categorize.
Example: "The documents were in such disarray that it was almost impossible to sort them into the correct files."
Alternatives: "nearly unmanageable to organize" or "practically impossible to arrange."
The movie is packed with information and attitudes that are almost impossible to sort out.
Care for elderly people is one of those things that's not hard to sort out, given money, and almost impossible to sort out without it.
It is almost impossible to sort out why Louis, the founder of the company, did not sign the 1972 lease for the new store or join the newly formed corporation.
At one point in Lyndall Gordon's biography she says, "There's no getting to the bottom of Vivienne -- at this distance in time, truth and untruth lie so close that it is almost impossible to sort them out".
But in comic operas it is almost impossible to sort out how much of the comic effect is derived from the book and how much from the music; and the highest forms of musical humour, the unexpected delights of a lighthearted scherzo by Mozart, defy verbal analysis, unless it is so specialized and technical as to defeat its purpose.
The huge, close-set eyes of many types of lemurs serve to clarify the complexity of dark, dense close-up foliage, which, if the head is kept still, is almost impossible to sort out without stereoscopic vision — and in a jungle full of illusion and deceit, stereopsis is indispensable in breaking camouflage.
This makes it almost impossible to do any sort of systemic analysis, either in an academic or industry led way.
The main exception to this generalization applies to fauna, so drastically altered that it is almost impossible to know what sort of animal geography would redevelop in the areas of the United States if humans were removed from the scene.
It's almost impossible to have any sort of economic stability in the face of political turmoil.
