I played the demo before sharing without filling a form to manually send it to devs was added and didn't realize I wouldn't be able to play or upload my dungeon now that it's released so here's my dungeon which one of the devs(adrian) mentioned loving.
https://mega.nz/file/J1tGlYQL#dWVLE_FyVRN2iUpPMrH4tJRza9j_5i1YHdd0E9HLhP0
just extract it to AppData\LocalLow\FIRECHICK\SuperDungeonMaker\LocalDungeons

Anyway while it isn't as easy to use I for the most part decided to switch to using Solarus Engine to do stuff like that.

"If you like it, BUY IT!"

Or deal with it.

buy the game and say it to the developpers

You can download dungeons though (at first I assumed it just includes all the dungeons made before release but looking at https://superdungeonmaker.mod.io/ and comparing with latest ingame dungeons it doesn't seem like that's the case)