I had to look up Blynk - it appears to be a software package that consists of an app for iOS and Android plus libraries for Arduino that allow an internet-connected Arduino to be controlled from the iOS/Android app.
Since Flutter is an Arduino, it seems reasonable to expect that if it was internet-connected (through a WiFi or Ethernet or 3G/4G or even through USB to an internet connected PC) then this would work. But I am also about as new as you are and someone would need to try it. Maybe I will do that this evening. I would have to use the USB connection because I don't have any of the other options.