While Lily was a beloved character on the show as well, the Sex Education season 4 Ola absence had a bigger impact. Sex Education was known for its extensive cast of colorful characters with Ola and Lily emerging as two of the best on the show, thanks in no small part to their charming romance. Sadly, with several cast exits before the final season, neither Lily nor Ola returned for season 4. While this is a shame in both cases, only Ola's absence will present a major story concern due to her close relation to the main cast, particularly Otis and Jean Milburn.

https://screenrant.com/sex-education-season-4-lily-missing-ola-problem/