FUT -> Friendlies -> Online -> Public co-op matchmaking (first option to the left)
Most likely unobtainable as of March 2022.Refer here:
https://trello.com/c/kJCLt00E/174-fut-public-co-op-matchmaki...Edit: it crashed to FIFA main menu on the day I originally wrote this but now matchmaking starts, it found me a partner even but the waiting time to find rivals is veeery long and I'm not sure if it's due to a bug or a low number of players in this mode. To investigate.
Edit2: I managed to find a game and won it, got the achievement (I have FIFA only on Origin tho). So I confirm, this works but it might be a struggle to find a game.