How to use Autopilot in plane without one?

No, I wasn’t sure what’s what outside the commands I bound. I don’t care about the Vertical Speed setting, I don’t want it to go up and down, I’m not trying to get it to follow a flight plan, I just want it to hold what is. I’m afraid there’s no capability for that, though.

This is the ONE area where 2D panels were useful in FSX, to add functionality occasionally used that’s not on the panel.