That same year, Efira was part of the ensemble cast in the comedy "Sink or Swim" directed by Gilles Lellouche, which was screened out of competition at the 2018 Cannes Film Festival, and earned her a Cesar Award nomination, for Best Supporting Actress. Also in 2018, her performance in the drama "Keep Going" was praised, with "The Hollywood Reporter" writing that she "is excellent here as a woman caught between her fiercely independent nature and her desire to be a good mother, trying to steer her son on the right path". The following year, Efira starred in the comedy-drama "Sibyl", her second collaboration with director Justine Triet, playing a psychotherapist who wants to return to writing. The film was selected to compete for the Palme d'Or at the 2019 Cannes Film Festival, where it received mostly positive reviews with particular praise for Efira's performance. "Variety" stated that ""Sibyl" seals the arrival of Efira, once pegged as a likable but lightweight comedienne, as a first-class leading lady of consistently expanding range and elan — with the emotional honesty and deadpan pluck to pull off the more outrageous character turns in Triet and Arthur Harari’s limber original script." while "The Hollywood Reporter" felt that "the actress plays several roles at the same time — the astute psychologist, the struggling author, the affectionate yet neglectful mom, the fervid lover in two very candid sex scenes — and she does each one extremely well, turning Sibyl’s altered states into a whole that reflects her drive to be many things at once."