https://www.pcgamer.com/rocket-leagues-new-leveling-and-xp-system-is-now-live/

Psyonix has rolled out a major "Progression Update" for Rocket League that completely revamps the game's progression system (hence the title) and eliminates the level cap. The update also adds a new "Clubs System," new achievements and trophies, and makes numerous "quality of life" improvements as well. 

The update, teased in June, changes how experience is awarded—it can now only be earned in Online Casual and Competitive Matches, and will be based primarily on match length rather than score—and how levels are gained. Instead of it "taking progressively longer to earn" levels past 20, successive levels will require a flat amount of XP, and the cap at level 75 is gone as well, so you can climb as high as you want.