Yeah, the software apparently used for demixing in this instance can't separate something like two guitars recorded on the same track, or at least it couldn't when it was used extensively for Peter Jackson's Get Back. He demonstrated its' capabilities in an interview at the time, taking a mono Nagra recording of an 'I've Got A Feeling' rehearsal and separating it cleanly into drums, bass, voices and guitars IIRC. These could then be balanced and EQd separately in order to make a much more satisfying stereo image.
If, say, that technology (reportedly far better than Abbey Road's in house version) were applied to 'Taxman', the track layout of which
@dobyblue has kindly provided above, it can be seen that the main problem lies in the fact that drums, bass and one guitar were recorded directly onto one track right at the beginning...other, later overdubs present less of problem.
The software would in this case be capable of separating drums, bass and the guitar into separate tracks.
Other songs present similar problems, e.g. 'She Said, She Said' where drums and bass were initially recorded together on one track with two guitars on another.