It's been established in that, on Gallifrey, only Time Lords have the ability to regenerate, while lower born Gallifreyans don't have the same luxury.

Source: https://screenrant.com/doctor-who-time-lords-war-regeneration-weapon-theory/

The Doctor is the nameless guardian of Earth, the savior of worlds, and a member of an alien race, the Time Lords of the planet Gallifrey.

Source: https://screenrant.com/doctor-who-tardis-facts-trivia/

While the Doctor has visited many different worlds over the decades, the show's most iconic fictional planet is probably Gallifrey.

Source: https://gamerant.com/best-fictional-planets-in-tv-shows/