No, they're not...
"Most of the reported cases that occurred after vaccination had an uneventful course. The take-home messages from the two studies may be that clinically suspected myocarditis is temporally associated with the BNT162b2 mRNA vaccine but is rare, is more common in young male patients, and (with a few exceptions) is self-limiting. As acknowledged by the authors, temporal association does not imply causation, and the risk of vaccinal myocarditis is very low. The results of these two studies are valuable for doctors, patients, and the public to reduce the fear of myocarditis as a reason for excluding young people from vaccination, especially since myocarditis has also been temporally associated with Covid-19."
Presenting that article as an argument against vaccine safety is specious, considering the article actually concludes the risk of vaccine-induced myocarditis is extremely low (~2 in 100,000, based on the assumptions that all suspected cases of myocarditis were actual, and that they were caused directly by the vaccine, neither of which the author can confirm, but assumes for the worst-case scenario), and fatal cases are especially rare (one in 5 million). You're more likely to die of COVID (1.6% CFR in the US) than to have a mild self-resolving case of myocarditis from the vaccine (0.002%).