What's peculiar about F21-F24 keys on MacOS? I observed some questions on the Internet concerning this.

F20-F24 keys do not respond, but are mapped
https://forum.keyboardmaestro.com/t/f-keys-f13-to-f24/8953
https://discussions.apple.com/thread/1090226

Karabiner-Elements can map from F1~F24, but can only map to F1~F20
And you can tell the OS is aware of there keys from this reply: https://forum.keyboardmaestro.com/t/f-keys-f13-to-f24/8953/7
So what's peculiar about F21~F24 on MacOS?
If this post at the Hammerspoon GitHub site is right:

then macOS does not handle F21~F24 (0x70~0x73) at all.
And it makes sense for Karabiner to not deliver any of these keys to the OS because of that.