I have determined this to be a lack of input overrides in the udev hwdb.d 60-keyboard.hwdb definition. For now, I have declared the following in my /etc/udev/hwdb.d/90-apple-keyboard.hwdb, which I'll attach. It may or may not be accurate for all Apple keyboards.
** Attachment added: "User settings override for udev hwdb for Apple keyboards" https://bugs.launchpad.net/ubuntu/+source/plasma-desktop/+bug/1806321/+attachment/5221670/+files/90-apple-keyboard.hwdb -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1806321 Title: Multimedia play/pause, skip forward, skip back keys not working To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/plasma-desktop/+bug/1806321/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
