As observed by others, you need to be extremely careful assessing whether the real level of cardiac issues in spectators or players has changed over time, or if the *reporting* of it has changed. I'm not aware of any reputable research on this, but it could well exist somewhere.
Then, even if it has changed, need to understand why. *If* it is COVID related, it's overwhelmingly likely to be associated with infection rather than vaccination, given what we know of the relative risks from very well controlled clinical trials and extensive real world evidence.