Summary and some discussion here: https://www.nextbigfuture.com/2023/08/myocarditis-heart-damage-in-1-out-of-35-covid-vaccinations.html :

"A new study of 777 people found that 22 had markers that indicated the mRNA-1273 covid vaccine caused myocardial injury in 1 out of 35 people. This is about thousand times more than prior estimates of myocardial injury. It would mean if 1.8 billion people in the world had covid vaccinations and boosters then 50 million would have had myocardial injury. This would usually be mild and transitory but if those people had strenuous exercise during this period they could trigger heart attacks. This would mean if 280 million people in the USA had covid vaccinations and boosters then you would expect about 8 million to have experienced myocardial injury from the vaccination."

Here is the source study: https://onlinelibrary.wiley.com/doi/epdf/10.1002/ejhf.2978

Dr. John Campbell discusses the new study: https://www.youtube.com/watch?v=cd_RTf_ForA&t=80s

I am not an expert but this study looks pretty legit to me: peer reviewed, relatively large cohort (777 people), respectable source and so forth.

If the risks revealed therein are in fact indicative of the population risks of these vaccines this is enormous news and a real "smoking gun" moment.

Edit: Here's a video of Dr. Vinay Prasad giving a very good explanation of the study (thanks to @fauxgnaws): https://www.youtube.com/watch?v=vveMHtVk_mY