Hi everyone this is very strange.

No matter what I put in my game (empty scene or very heavy scene with thousands of object, tens of textures etc…), the build size is always 625kB.

Seems like a bug but the game works normally each time.

Any idea? Thanks in advance!

So you game is always 625kB even when you build it? This isnt possible, make sure you check the file destination of the build, that should have the actually size (see image)