Chrome has started removing support for certain "powerful" features (e.g. camera/microphone access, offline support, etc) from HTTP and requiring HTTPS for them, with the exception of localhost where they can still work for development purposes. However this causes a problem with preview-over-wifi which is treated as insecure access and these features get disabled. I guess they just added fullscreen to the list.
There is a workaround which involves using Chrome dev tools port forwarding to set up a localhost URL on the device itself which really forwards to your PC, but it might be easier just to leave it not in fullscreen and just test that last bit after exporting to a HTTPS host.
There is something strange here, I can get full screen with these conditions.
Fullscreen in browser: letterbox integer scale (does not work with other options)
If I touch the screen in an uncovered area, a black area (Lower black area of the screen, in landscape mode) , the full screen is successful with browser object.