@SGaist I'm not familiar with "movement direction feedback", but it very well could be that.
It should be supported indeed. Did you try with a more recent release of Qt ? Like 5.15 or even 6.2 ?
The problem was in the Windows firewall. I still don't understand why this was affecting the sound, but disabling the firewall did the trick.
Found the problem: I had installed Qt v 6.0.0 with emscripten 1.39.8. documents say 1.39.8 should work with Qt v5.15.0. Works after installing the correct Qt version.