[micromacrofoot]

The abstract from your linked paper seems to indicate the risk is minimal.

>According to the US Centers for Disease Control and Prevention, myocarditis/pericarditis rates are ≈12.6 cases per million doses of second-dose mRNA vaccine among individuals 12 to 39 years of age

That's a 0.0013% chance of getting something that "almost all" patients had resolution of with or without treatment:

>Almost all patients had resolution of symptoms and signs and improvement in diagnostic markers and imaging with or without treatment. Despite rare cases of myocarditis, the benefit-risk assessment for COVID-19 vaccination shows a favorable balance for all age and sex groups; therefore, COVID-19 vaccination is recommended for everyone ≥12 years of age.