That's really a shame! Using a hex editor, I was in fact able to verify that the submitted executable is the same as unity's standard launcher, apart from some changes in metadata. In that case, it is entirely necessary to include the _Data, Mono (or IL2CPP) directories, and any DLLs. If you are set on uploading a single executable, might I suggest an auto-extractor like "iexpress" which comes built into windows, or possibly 7-Zip's "SFX Archive" feature. I would have loved to see what this game was!