Some teams don't work every day of the week so counting reporting on those off days is mostly unnecessary. Shortcut has a Workspace level setting that allows an Owner or Admin to set certain Working Days.
All calculations, metrics, and lines on the Burndown Chart take Working Days into account to give you a more accurate representation of your work. The Default Working days are Monday through Friday, inclusive.
Currently, only the Burndown Chart accounts for non-working days, but the rest of the charts will be updated soon.