Flask's documentation [https://flask.palletsprojects.com/en/2.2.x/deploying/] recommends that when deploying, one should use a dedicated WSGI server rather than the built-in development server. Additionally, running an HTTP server (such as nginx) in front of the WSGI server can be safer.
One additional advantage of this may be that it becomes easier to serve compressed (gzip or brotli) content, so for example, the Unity WebGL build (which is currently uncompressed) could be made much much smaller.
Perhaps try Gunicorn as WSGI server and nginx as HTTP server.
Flask's documentation [https://flask.palletsprojects.com/en/2.2.x/deploying/] recommends that when deploying, one should use a dedicated WSGI server rather than the built-in development server. Additionally, running an HTTP server (such as nginx) in front of the WSGI server can be safer. One additional advantage of this may be that it becomes easier to serve compressed (gzip or brotli) content, so for example, the Unity WebGL build (which is currently uncompressed) could be made much much smaller. Perhaps try Gunicorn as WSGI server and nginx as HTTP server.