There has been few crossovers of two worlds in combat sports that has started a huge debate that is an MMA fighter vs Boxer who wins? While there is no perfect answer for that, let's just take a look at some UFC fighters who competed or will compete with a boxer.
Holly Holm has a professional boxing record of 33-2-3 (W-L-D). It's safe to say that every UFC fighter who faced Holly Holm has faced a professional boxer.
UFC fighter Randy Couture fought professional boxer James Toney on August 28, 2010 at UFC 118. Couture won the fight via Submission (arm-triangle choke) in the first round.
McGregor fought the undefeated professional boxer Floyd Mayweather in a boxing match. This fight took place on August 26, 2017. Mayweather won the boxing match via TKO in tenth round.
Former UFC fighter Ben Askren is scheduled to fight youtuber turned boxer Jake Paul on 17 April, 2021.
Former UFC heavyweight champion Frank Mir will fight on the Ben Askren vs Jake Paul fight card against Steve Cunningham on 17 April, 2021.