TL:DR It's a pre-print, and the authors themselves recognize the problems with it - see below. Until it's peer-reviewed and published it's just opinions, like the website says: "The statements, opinions, and data contained in all publications are solely those of the individual author"

Consider this folks:

• The study the impostor is linking to says: "With approximately 98% of the King County population having received at least one dose of a COVID-19 vaccine, nearly the entire population was exposed to the variable in our model."

So it's not like they were comparing vaccinated people to unvaccinated people.

We know that the risk of myocarditis from covid is about seven times higher from covid that from the vaccines. Legitimate science studies have shown it, and the study the impostor is linking to recognizes that this and other factors are involved:

"There are multiple potential, unaccounted confounding variables, such as changes in healthcare access, variations in public health interventions, socioeconomic factors, drug use, and COVID-19 infection that could have influenced cardiopulmonary arrest outcomes"
AND
"COVID-19 infection and pandemic-related emergency care disruptions may have also contributed to the increase in excess cardiopulmonary arrest deaths"
AND
"our models may be unstable due to containing few data points."

So the infection causes heart problems but some people and their useful idiots want to ignore that, and only talk about the vaccines.