I am rather new to the platform, so sorry if this question has an obvious answer.
I am organizing a game where people gets points when they organized an event and people get points when they participated to the event (max. of 12 participants). The participants are set in a multi-dropdown.
If you want to create the things in the multi-select, right after save button is pressed and not while they are being selected, you can check this answer: Adding Multiple Things to Data type - #2 by hergin
There is no bulk create a thing in the regular workflow actions. So you should probably do the trick or find another workaround.