Try testing it in a different browser; Chrome seems to work the best for Unity web builds, so try that if you haven’t already.
Otherwise, it might be something to do with your z-ordering. I have had similar issues with Linux and Mac OS Unity builds in the past and it was usually related to z-ordering of 2-D elements. Make sure all of your 2-D sprites and backgrounds have the correct z-order: Things that should be in front should have higher z-values.
As to the sound, make sure itch.io has permissions to play audio through your browser and your tab and browser aren’t muted.