I think this is the correct link:
https://chickenmag.com/swedish-blue-duck/
But, basically it looks like a blog. Blogs are notorious for misinformation.
According to the livestock conservancy they are on a watch list. But, so are a lot of other ducks. Some say if you aren't breeding true to the breed standards, then you aren't helping the breed to break out of the watch status.
Heres the definition of watch from the conservancy:
Watch: Breeds that present genetic or numerical concerns or have a limited geographic distribution, with fewer than 2,500 annual registrations in the United States, and an estimated global population less than 10,000. For rabbits, fewer than 200 annual registrations in the U.S., estimated global population less than 2,000, fewer than 500 recorded at rabbit shows in the previous 5 years, and 31-60 breeders. For poultry, fewer than 5,000 breeding birds in the U.S., with 10 or fewer primary breeding flocks, and an estimated global population less than 10,000.
The list of livestock animals:
https://livestockconservancy.org/heritage-breeds/conservation-priority-list/
Specifically swedish ducks:
https://livestockconservancy.org/heritage-breeds/heritage-breeds-list/swedish-duck/