Oculus only test their branch for Oculus Devices and the Oculus Runtime. There’s no intention to have the two branches “unified”. We always recommend you use UE-Main as we can’t help or try and reproduce your issues if that’s the branch you’re using.
The OculusOpenXR plugin has been removed in 5.0-Release as Oculus rolled their OpenXR support into the OculusVR plugin. In Project Settings → Plugins → OculusVR there’s now a setting to select which “plugin” you’re using: Legacy, OVR OpenXR, or Native OpenXR:
All of the features available in the Legacy OVR plugin doesn’t have counterparts in OpenXR yet and that’s why you’re still seeing the Legacy OVRPlugin as an option. Work is ongoing to deprecate it in favor of 100% OpenXR support.