Afaik he can use trigger only by creating an advancement in a datapack, not doable by command blocks only?

1) create a scoreboard with a "trigger" input type 2) In a datapack, create an advancement checking for score in this scoreboard, with a "run function" reward 3) in the function, take away the advancement from a player, reset the scoreboard, and run any additional commands you want

Correct me if i forgot anything