The application manifest MIME type is
application/manifest+json.If the protocol over which the manifest is transferred supports the [MIME-TYPES] specification (e.g. HTTP), it is RECOMMENDED that the manifest be labeled with the application manifest MIME type.
From the Web Application Manifest specification (W3C Editor’s Draft 09 March 2021).
The Content-Type header for files with the .webmanifest extension should be application/manifest+json instead of application/octet-stream. Read the specification for more information.
