Well look, if push comes to shove, I'd rather like to put the Timeless Child link in the "More ambiguous" section myself! Again, from a strictly in-universe point of view, we only have the Master's word that the Timeless Child became the Doctor.
But conversely, if you're going to want to lean on the obvious out-of-universe intent that the Doctor is the Timeless Child, then you should also lean on the obvious intent of placing that Brain of Morbius quote in the intro of Lungbarrow, namely that the Other is very strongly suggested to have been the Morbius Doctors.
(The quote "You can't… not that far back… not even I" from the Brain of Morbius novelisation, while nothing definitive, also seems to suggest the Other more than the Timeless Child, since it frames the Morbius Doctors as a past that the Doctor is aware of, but wants to suppress, rather than a past which has been forcibly suppressed and which the Doctor leaps at the chance of rediscovering the moment she learns a hint of it.)