I'm guessing these things are covered somewhere in the hundreds of posts here on the "All Things VR" topic but they are scattered all over and the search function sucks on this forum. Not sure why nobody has stickied a post on how to get things going correctly?
Here is what I learned while setting up an Oculus Rift S this week. This is what worked for me, you may be different.
1. You must use AH3 DX11 version (DX9 version did not work for me).
2. No need to start Oculus or SteamVR first, just run AH3 DX11 and you will get a prompt to use VR, select yes.
3. Map a key or switch to center your VR headset view. Hit that after launching AH3.
4. View Setup:
The 6 O'clock view can be difficult with VR so map a hat switch L and R to Left FRONT and Right FRONT view (worked much better than the settings that most people suggested to me of Left REAR / Right REAR or even pure 6 oclock view mapped to a button). The L/R frontal view gives a much smoother transition when tracking a con and allows you to see your 6 o'clock view with minimal head twisting.
Also, after mapping your L/R hat switch, hold hat switch left then lean out left and sit up in your seat. Hold that position and hit the F10 key to lock that view in to you left view. Repeat for right view. Now when you look rearward you should have a much better view with less headrest blocking your view.
5. Get VoiceAttack - the program. Works great for keyboard commands and macros when you can't see the keyboard with headset on.