The nose-up and nose-down buttons on the autopilot paired with the G1000 in the Cessna 172 and DA62 aircraft are reversed. The bug probably affects all G1000-equipped aircraft.
When the autopilot is engaged, and FLC (Flight Level Change) is in use, the nose-up button should reduce the target speed, and the nose-down button should increase the speed. The on-screen tooltips, as well as the actual behavior, is currently the reverse of the correct behavior.
This bug has existed since the very first release of FS2020.