The fourth vaccine to receive approval in parts of Europe, the Novavax shot, hasn't had any reports that I could find of myocarditis.
Disclosure : I hold no position in NVAX, short sell or options. I also don't hold Takeda Pharmaceuticals, at either their US listed shares or CFDs of their Tokyo listing.
I'm more inclined to believe that the danger from the nanoparticle had to do with it delivering the mrna to places it does not belong, such as the heart and brain, rather than the mrna itself