As well as pressing and holding Command, or Pressing Globe + M to bring up the keyboard commands window, pressing Globe + Control + option does so too. Pressing these keys combined with the left and right arrow keys should take VoiceOver to the first or last item, and so the two commands are in conflict.
Press Globe + Control + Option keys together.
The keyboard hints window will pop up.
If your intention was to use these keys in combination with the left or right arrow, in order to go to the first or last item, you may find the two commands are in conflict.
Make sure to press the Control and Option keys down before the Globe key if your intention is to combine with the arrow keys.