You might want to take a look at this article from the NIH. (Nation institutes of Health).

Cardiomyopathy is estimated to affect about 1 in 500 adults, and many cases may go undiagnosed. While it can occur at any age, sex, or race, certain types are more common in specific populations, like dilated cardiomyopathy in Black people and males. Hypertrophic cardiomyopathy, the most common inherited type, is estimated to affect 1 in 500 people worldwide.

Research consistently demonstrates that Black individuals tend to have lower serum selenium concentrations compared to their White counterparts.

Selenium supplementation might offer benefits for individuals with cardiomyopathy, particularly if they have a selenium deficiency. Studies have shown that selenium deficiency can contribute to dilated cardiomyopathy, and in some cases, selenium supplementation has been found to reverse the condition. However, more research is needed to fully understand the role of selenium in preventing and treating cardiomyopathy, especially in cases where deficiency is not present.

Selenium is an essential micronutrient that plays a role in various bodily functions, including heart health.

A condition called Keshan disease, a form of dilated cardiomyopathy, is linked to selenium deficiency.

In Keshan disease, selenium supplementation has been shown to mitigate clinical manifestations and even reverse the condition in some cases.

Some clinical trials have shown improvements in clinical symptoms, left ventricular ejection fraction, and lipid profile with selenium supplementation in heart failure patients.

Not sure why medical professionals don't consider these findings.

Keshan disease:
In regions with very low selenium intake, a severe condition called Keshan disease (cardiomyopathy) can occur, according to the National Institutes of Health.

Globally, an estimated 500 million people may be deficient in selenium.