The Mega + WiFi R3 is not in the official list of supported hardware:
but the search results I pointed to earlier seem to show Blynk community members using it successfully.
It’s not the type of hardware that I personally would choose to buy - because it’s expensive, bulky, has limited processing power and has to be physically connected to a computer to update it (no Over the Air update capability).
If you haven’t already bought one then I’d suggest that you read this:
If you have already bought one then look at the search results and see what everyone else is doing with them.