Timeless Child's realm

In an account which the Spy Master claimed to have discovered in the Matrix, the Timeless Child, who would become the Time Lord known as the Doctor, hailed from a realm which was potentially a separate dimension or universe from N-Space.

The child, the only known member of their species, was found near a boundary to their realm, from which they had come through, seemingly having been dumped on a random planet near a monument. Ultimately, the child was found and taken to Gallifrey by the Shobogan Tecteun, though their true place of origin remained unknown to the Gallifreyan explorer. (TV: The Timeless Children)

When retelling the story she'd learned from the Master, the Thirteenth Doctor explicitly identified the realm on the other side of the mysterious portal as being "another, unknown dimension". (PROSE: The Secrets of the Timeless Child)