More often than not, Eucharistic miracles reinforce the faith of those who already believe.
I visited two Eucharistic miracles while on a pilgrimage in Italy. Some time after returning home I gave a day retreat to a group of Secular Franciscans who were mesmerized and delighted by the presentation. Preaching to the choir, as we say. Someone who is not a Christian would likely have dismissed it all.
The only distinctive example of someone being truly convicted by something like this that comes to mind is one of the original members of the team investigating the Shroud of Turin, who was Jewish and then became Catholic through the study of the Shroud.
And, we know there are plenty of people who think the Shroud is a fake. I like how Benedict XVI referred to it as “an icon written in blood.”
Skeptics will always find a way to rationalize their thinking.
We see the proof of that as Jesus raises Lazarus, and of course, in His own Paschal Mystery. "Even if a man should rise from the dead . . . "