These link might be helpful:

1. https://docs.google.com/document/d/11PbA99z8nzLUIk1766KZAkrmRaj0wRQQx07x6RQMzlk/edit
2. Community post

You can try with random number generator and than matching number against this number. 

Thanks for your fast replies! It might work, but I’m actually looking for a way to implement the choice dilemma as sketched below: For each of the 21 decision pairs, participants will have to select option A or B. 

It currently comes to mind that it might be easiest to add an extra column where participants can select option A or B. Better ideas are welcome, of course I’m very very new here. 

We can use loop & merge as well.

Yes agree with Shashi, loop and merge can be good solution. You can refer details here

https://www.qualtrics.com/support/survey-platform/survey-module/block-options/loop-and-merge/

Thank you! I’m positively surprised by all the help received so quickly in this community ^^. I’ll try to figure things out, and otherwise get back to you ;)