TLDR! → Hit “i” to toggle the ‘punch in point’ and hit “o” to toggle the ‘punch out point’. These things are the two halves of the red arrow.
(POSSIBLE) HOT TIP! → To all you following at home this afternoon or anytime in the future when Cubase is not recording $|-|i+ and it doesn’t make any sense: Little Red Arrow on Time Bar: Automatic Record