He scored four tries in Munster's 54–11 away win against Italian side Zebre in round 6 of the Pro14 Rainbow Cup on 11 June 2021, which saw Coombes finish with 15 tries in his 22 appearances for Munster during the 2020–21 season, and equal the Munster record for tries scored in a game (tied with Mike Mullins (2001) and Alex Wootton (2017)). In total, Coombes racked up 1,310 minutes for Munster during the season, and averaged a try every 87 minutes. In recognition of his performances throughout the 2020–21 season, Coombes won the Munster "Player of the Year" award, becoming the youngest ever winner of the accolade.