Please consider registering media types to the Internet Assigned Numbers
Authority (IANA) before requiring their inclusion in /etc/mime.types.

https://www.iana.org/form/media-types

Simplified registration procedures for vendor and personal trees have been
implemented since RFC 6838, that states: "it should rarely, if ever, be
necessary to use unregistered types."

https://tools.ietf.org/html/rfc6838

I have confirmed that the process is fairly quick and painless by registering
various media types in 2012, 2014 and 2020.

 -- Charles Plessy