Yes, but ration them — sunflower seeds are safe yet so fatty and addictive that parrots will eat them to the exclusion of everything else.
What it means for macaws
Macaws tolerate fat better than smaller parrots, so sunflower seeds can be a more legitimate part of their diet than it would be for a budgie — still in sensible amounts, and never salted. Macaws can handle a generous portion for their size.
The full picture on sunflower seeds
Sunflower seeds are the potato chips of the bird world: high fat, high reward, low effort. A seed-junkie parrot eating a sunflower-heavy mix is on the road to obesity, fatty liver disease, and malnutrition — the classic diet problem in budgies, cockatiels, and conures.
A few seeds a day, ideally hand-delivered as training rewards.
Unsalted, unroasted, ideally in-shell for the foraging work.
Especially strict rationing for budgies and conures prone to obesity.