In https://vincentgarreau.com/particles.js/ qtwebengine performs much worse than Chrome on Windows. It will only stay at the minimum level and run at 45fps.
It is not a problem with the acceleration though as we can type in the same numbers Chrome reaches, and we can run those much more complicated graphs at an equal 45fps.
Lowering the complexity also changes nothing and it remains at rougly 45fps.
The assumption is that we do not deliver a clear signal for the next frame fast enough to make self animation JS render at 60fps