To unlock the Kompetitor trophy in Mortal Kombat 11, you will need to play 50 Kasual Versus matches. It doesn't matter if you win or lose, completing 50 will unlock the trophy.
To fight Kasual Matches:
Main Menu > Fight > Online > Versus and make sure that Kompetitive Mode is set to off.
You can track your progress towards this trophy:
Main Menu > Kareer Stats > Online > History > Kasual Matches Played