Sorry, you are not allowed to upload this file type.

I went in the plugin settings and enabled the “.zaz” file type. I then tried to upload a zaz file and “Sorry, you are not allowed to upload this file type.”

I have tried other files with official MIME type specifications and get the same error.

I have gotten “xz” files added with MIME type application/x-xz but nothing else I have tried works.

.c, .cpp, .cxx, .h, .sh, .patch, .xml, .py, .ini, .eepm, etc, etc, etc… None of them work at all no matter what MIME type I try to set.

I even tried to hack the types directly in to WordPress and still can’t get it to work. What is going on?

The standard base image/video and some archive types work fine. Where is the root list of MIME types stored at? There is obviously something outside of WordPress or plugins that is determining the actual available types.

Running WP 5.9.1