I’ll note that a personal shield would not be enabled all the time.
Dune notes several limits to them: limited charge, they restrict movement and hearing, and the shield also limits gas transfer so over time air within a shield becomes stale and uncomfortable if not deadly. All irrelevant for short combat, but for long term use, such as guard duty, these are problematic.
That said, if one manages to sneak up behind someone who has active shield, one might as well use a knife. Would be more silent than a projectile weapon if nothing else.
In regards of the topic in general, i think that projectile weapons are not in use in general within the Imperium. Obviously the concept exists, so perhaps they can be found in museums and hunting weapons or the like. But for warfare in general, no, because of the rules of War of Assassins and general reliance on shields (and when shields are not used, laser weapons seem to be the go-to weapon). And not just shields, but also to avoid collateral damage. Projectiles have tendency to be indiscriminate.
Prisoners, slaves, rebels, etc. probably do use projectile weapons because manufacturing such isn’t a too difficult task. It just doesn’t work in most worlds that have professional garrisons equipped with shields.
Arrakis and the limits it imposes on shields make such weapons practical for the Fremen.
I don’t think projectiles are used even for space warfare/anti-starship weapons in style of the new film. While cool imagery, there’s some fridge logic to it: Personal shields are noted as requiring velocity of 6-9 cm/s to be pierced. If that is universal limit, achieving that in combat seems implausible without advanced computer controlled systems, which are obviously a no-no in Duniverse. If it is not universal limit, the piercing velocity could be even slower. (Consider the task of landing a rocket like Falcon 9, how tricky it is. Piercing a shield in space combat is harder task because everything’s moving, not just the rocket.)
Exception would be if a spaceship shields protect only a part of a ship, and can be overwhelmed by sheer firepower. Monitor type warships are noted to mount heavy armor and shield protection, which seems redundant at a glance.
(Since laser reaction can affect the shooter, they don’t seem to be good options in space combat against shielded opponents.)
No comment on how exactly space warfare can be even conducted with these limits. But then, there’s little reason to do in the first place.