UFC President Dana White is ready and willing to make a fight between Jon Jones and Brock Lesnar happen, per TMZ Sports.
White told TMZ "he's heard the rumors" and said "if Brock is 'seriously interested' in fighting Jones, he's more than happy to put it together."
Lesnar has split time between WWE and UFC over much of the past two decades. He was most recently under contract with WWE and fought at WrestleMania 36, but he's no longer under contract with the promotion, per Mike Johnson of PW Insider.
Therefore, he is hypothetically free to fight in the UFC, even if it's for just one bout.