After retirement at the end of the 2018/2019 season, after some improvement in health, he returned and competed in some of the second-tier, Challenge Tour. Now an amateur in status, Muir was able to enter the 2020 European Masters, but lost in the first round of qualifying to Kurt Maflin, 5–2. Muir reached the semi finals of 2020 WSF World Championship in Malta and EBSA European Championship in Portugal.