None of those settings/actions will affect the problem you’re encountering with mjs files; be careful about changing unrelated settings/code, as you might cause problems elsewhere in the system.
If you are seeing the warning in your browser…
…then your web server needs to be configured to serve .mjs files with the application/javascript MIME type. Nothing else will fix the problem. This configuration is done outside of OJS, at the web server level, and the details of how to do this will vary from host to host.
Regards,
Alec Smecher
Public Knowledge Project Team