I have no knowledge of Flutter App development, but Azure Media Services can stream HLS or DASH to any player that supports those protocols.
Sounds like you just need to find a supported player framework in Flutter that can handle HLS or DASH. I see that there are some users out there on Stack Overflow that have succeeded with Media Services -
See this one - https://stackoverflow.com/questions/61833045/adaptive-hls-streaming-flutter-video-player