I've run into an issue where I can no longer insert BMP image files, using either the TinyMCE file picker or the standard file picker.

Replication steps:

1. Go to any course
2. Find an existing or create a new section, then edit it
3. Attempt to attach a bmp image either using Tiny file picker, or the standard file picker

Observed: See attached video

Expected: The bmp file should attach without error

Note: When you go to https://sandbox.moodledemo.net/admin/tool/filetypes/index.php

The file type is listed there, which brings me to assume it is indeed supported.