As a WebGL platform, Unity 6 version worked normally when built and run, but in Unity 6 alpha version, the following error occurs when built and run.
“Uncaught SyntaxError: Failed to execute ‘querySelector’ on ‘Document’: ‘0’ is not a valid selector.”
Could you please provide more information about this issue?
The behaviour that you are observing might potentially be a bug in Unity. Could you please submit a bug report with a project?
Here’s the info on how to submit a bug report bug-reporting.