(1) The regenerative energy going into the 11th Doctor's mouth was the Timeless Child in a evolved energy form while being sent by the timelords, by Rassilon's orders and though the Division's influence, to make the 11th Doctor it’s host in a symbiosis way as a way to preserve it. That the reason the Doctor was able to regenerate into the 12th and 13th Doctor is because of the Timeless Child and using up all his lives is still a fact. That the Timeless Child is like a life support for the Doctor.
(2) The Master of the Roger Delgado era worked for the Division and the reason he did the things he did in that incarnation. The wanting order in the universe by controlling it while Tecteun knew about the drum beats, the beacon, and how it was slowly driving the Master mad. The Master (Sacha Dhawan) and Tecteun have their reunion after she saved Missy and made her regenerate and the Master knew about the true origins of the Timeless Child from Tecteun and their situation where the being turned into pure regenerative energy and needed a host to contain it and it was him who suggested the Doctor because he/she was an outsider. Thus the energy going into the 11th Doctor’s mouth. The Master also came up with the story that the Doctor was the Timeless Child, and even manipulated Captain Jack, because he knew his enemy was quite capable of using the truth as a weapon against his/her enemies and it was best to keep that advantage away from her. Also, like killing two birds with one stone, he was tasked to get rid of Gallifrey so they wouldn’t get in the way of Tecteun’s plans to move to the other universe where the Timeless Child came from. Oh’ and the portal to the Gallifrey was Tecteun’s and she used it to communicate with Rassilon like a phone line and e-mail, since Gallifrey was stuck in a moment in time which gave Tecteun the advantage over Rassilon when it came to a deal, since going in and out was impossible at the time and Tecteun had future knowledge on how to escape, and convinced him to send out the Timeless Child through the crack.
(3) The fugitive Doctor was really from a possible future, while having memory problems because of the Division. The Division must have captured the Doctor in the future. the things mention in Flux, like Karvanista and Ravagers are perhaps a possible future that only seem like the past because of time traveling which ends up with Gallifrey of the past to going after her, since it seems that the Division believe that they're above the laws of time.
(4) When Tecteun and Ravagers spoke to the Doctor, they were probably speaking to the Timeless Child, while the Doctor was seen as nothing but a host, and Tecteun, with manipulating and using the Timeless Child as a lab animal, is no doubt willing to lie, but she was probably telling the truth when it came to the Timeless Child when she/he had a physical body, and she was probably talking about what the fugitive Doctor did after she escaped again and was influenced by the Doctor. That Tecteun’s past is the 13th Doctor’s future.
(5) Rassilon and Omega were probably partners with Tecteun and knew about the Timeless Child, and perhaps his immortality trap in the 5 Doctors was a means to lessen the chance of someone discovering the Timeless Child, since rumors of a being of limitless regenerations was perhaps out there in the public, while it was mention that he had a dream of immortality. He once told the 12th Doctor that they didn’t know how many regenerations they gave him and it might be because the host thing is experimental. The fact that Rassilon left Gallifrey before it’s true destruction means that he could perhaps be still around and holds the actual truth of the Timeless Child. Perhaps even mock the “Renegade Timelord” for not seeing the plot holes in the story that was told to him/her, like the fugitive Doctor having a police box Tardis which happened to the 1st Doctor. Omega’s entrapment inside the anti-matter universe might have been a betrayal, I think the betrayer’s name was Vandekirian on behalf of Rassilon and perhaps Tecteun was in on it like a silent partner, while Rassilon and his followers’ madness of becoming beings of pure consciousness after the destruction of the universe (Ultimate Sanction) may have made him a burden to Tecteun. The Project Revenant that resurrected Rassilon may be connected to the Timeless Child.
(6) The return of Gallifrey. After the Time Wars and being freed from the time freeze, the Timelords decided to create a fail-safe in case disaster happens, especially the kind that ends them and that fail-safe resets everything to before that threat happened, like going back in time, but the system isn’t perfect and needs someone outside to get it working and Rassilon may hold the secret on how it’s done.
(7) On the run from his/her people again. The Timelords decide that the Timeless Child is too dangerous to exist, and since the Doctor is stuck with the entity, she becomes as target as well.