Hello,
I’m having some hard times finding the option to allow quarter rest in sextuplets rhythms.
What is the option I’m looking for, if it exists ?
Thanks 
Unfortunately you cannot at present either directly influence the grouping of notes and rests in tuplets, nor can you edit the durations or positions of rests in percussion kits. The latter limitation is the really serious one in this case, as it means you cannot select that dotted eighth rest and edit its duration such that it becomes a quarter rest. We know this limitation is a pretty serious one, so it will definitely be addressed in a future version. Sorry for the inconvenience in the meantime.
Okay, thanks for the answer