I'm so glad I found this post. I'm also developing in Unity 2019.4.21f1, Oculus XR Plugin 1.8.1, and using Unity XR Interaction Toolkit (0.10.0-preview.7), XR Plugin Management 4.0.1. I'm polishing up my game the next few months and plan to submit it to Oculus store for review in May 2021. I'll add back to my scenes OVRManager.
Sorry to revive a 2 year old thread. But if you're THE "mighty coconut" that gave us Walkabout Mini Golf, it would be awesome if you posted more of these kinds of posts. WMG is a perfect example of a beautiful, and smoothly running app on Quest and I'd love to know how you managed to get steady framerates without giving up things like nice looking shadows or having glitchy occlusion issues or flickering billboards.