The whole lasgun-shield interaction concept is one of the hand-wavy parts of Dune, kind of like the eagles in LOTR, or the ridiculously inaccurate laser blasters in Star Wars.
Shields in Dune are common defensive technology, which means that lasguns would almost certainly have to be outlawed altogether to prevent some random encounter from turning into nuclear apocalypse.
In the first movie, I think Villeneuve deals with it somewhat haphazardly. The use of a lasgun at the agricultural research station perhaps makes some sense because shields can’t be used in the open desert without attracting worms. On the other hand, they show lasers being used at the first Battle of Arrakeen in close proximity to other ships that are shown to have active shields.