Myocarditis is more of a problem for younger people anyway and that was happening before the vaccines.
This study tells us that the Covid vaccines are TEMPORALLY related to the Covid-19 vaccines.
This study tells us that suspected myocarditis are TEMPORALLY related to the Covid-19 vaccines.
The observations in this study has also been observed in studies in Hong Kong. See here:
https://pubmed.ncbi.nlm.nih.gov/34849657/
Conclusions: There is a significant increase in the risk of acute myocarditis/pericarditis following Comirnaty vaccination among Chinese male adolescents, especially after the second dose.