Hello there. I’m probably mostly known for my Matrix client FluffyChat which was one of the first Flutter snap apps. This snapcraft journey took a long time already. I have encountered and fixed several issues so if I now search online for fixing bugs about snapping Flutter applications, I sometimes just get directed back to my own apps as an example, how to workaround them. 
You can find my repository here: https://github.com/krillefear/fluffychat-snap
I have also published some other apps to the snap store like a flutter flashcards app and my former Ubuntu Touch apps like JotIt (while I have ported some of them from QML to Flutter).
Unfortunately I’m not known for answering questions in this forum. More for ask questions of broken stuff… But I get experienced every time I try to snap a new application like Distrobox which builds here: https://github.com/krillefear/distrobox (still without podman inside).
So… I keep investing hours and days on snapping applications while it has not worked out many times. This is your chance to appreciate my perseverance