For the most part, Heathrow doesn't do mixed-mode operation (where you have takeoffs and landings on the same runway). However, my understanding is that this is not for safety reasons, but mostly to give people living under the flight paths some periods of respite from the noise. They did use mixed-mode single-runway operation for a while during covid.

https://www.heathrow.com/company/local-community/noise/opera...