21 for a French Press? That's way too fine. Barzata's own site suggests at least 28:

https://baratza.com/grinding-tips/

I personally have it around 32-33. I don't remember if I got that from their manual or from somewhere online, but I haven't noticed any degradation in flavor from the larger grind. The whole point of investing in a quality burr grinder is being able to get a proper coarse grind; make use of it!

EDIT: A separate Reddit post (though by no means authoritative) agrees with my recommendation of above 30 for FP:

https://www.reddit.com/r/Coffee/comments/1k0uhb/is_there_a_c...