Is there a desirable platform? Should I build for WebGL? Android? Windows?

There's no desired platform. Make sure it's useable for windows user and can be uploaded onto itch. 
If you build your application for WebGL you'll allow the user to play inside of the browser instead of having to download and unpack the files on their computer.
Hope that helped

If you want more people to play your game, do a WebGL build, the ease of access will get you far more players and reviews than a version which needs to be downloaded.

You aren't limited to a single platform, though! You can put out WebGL and Android/Windows/Mac/Linux and so on, if you're confident the game will run well in all versions.

I think the most desired one would be webGL but if you can't, try Mac/Linux/Windows. Those are in my opinion the ones that will get you the most people to actually be able to play the game, especially the judges.

Thank you all for the quick response.

I'll make WebGL my main build and afterwards build for Android as well.

May the Lord bless you always.