#im trying to find another post that goes into intricate detail of a possible timeless child/other timeline

[humandisastersquad]

Basically the timeless child, after Tecteun had finished experimenting on them to find the secret to regeneration, became the Other (which makes sense since they're Not of Gallifrey) and helped discover time travel and found Time Lord society etc alongside Rassilon and Omega (and Tecteun). This is even kinda suggested in The Timeless Children

TECTEUN walking down a corridor -- at the far end, two Gallifreyan figures (with the collars up) in silhouette. We can assume these might be Rassilon and Omega.

THE MASTER: With Tecteun, they became a self-appointed ruling elite. And Tecteun proposed: that he gene-splice the ability to regenerate into future generations of citadel dwellers. It would become the genetic inheritance of them and their descendants. But he would restrict the regenerative process to a maximum of twelve times.

The timeless child became the base genetic code for all Gallifreyans within the citadel. The civilisation which renamed themselves, with characteristic pomposity, Time Lords. The foundling had become the founder.

Eventually, they become disillusioned with what Rassilon is doing and throw themselves into the Looms to be eventually reincarnated as the Doctor etc etc

Alternatively, here's another take that I found digging around my blog where the Other's 'death' was due to Rassilon mindwiping and constructing a new identity for them to then be a an agent of the celestial intervention agency division.