The resolution of the iframe is not well adjusted but I could play the game directly with the iframe url and in fullscreen.
In Unity you could also check "Decompression Fallback" below "Compression Format", your game will be playable in the itch app.
Regarding the game, I find the concept interesting and the little narration is fun. However I find that the gameplay of the black holes does not work too well. I didn't understand why sometimes they killed me and sometimes not.
I wish you the best for your next games