Excellent question, assuming Moodle 3.11, looks like fonts in a sub-folder are not supported given the way /theme/fonts.php is written to serve the fonts from the Moodledata folder, where they've been placed, I assume by the CSS processing process that deals with 'font:theme' and only appears to copy the font files that are then actually subsequently used by the CSS itself.
Themes
adding fonts in a subfolder
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