Windows mixed reality

Hay,

Is the 5K plus compatible with the Windows Mixed Reality Portal? I’ve been trying to use MSFS in VR, but it wouldn’t go into VR unless compatible with the portal. I have Windows Mixed Reality for SteamVR install too.

No. Two completely different protocols.

Microsoft (WMR) uses it’s own SteamVR wrapper (you already installed this) that makes the WMR ‘talk’ to SteamVR.
Pimax uses its own proprietary software to do the same thing (PiTool).

WMR uses ‘inside out’ tracking (cameras on the HMD to determine controller position) and Pimax uses the Lighthouse system (Vive, Index) with one or more base stations to track controller movement.

Two completely different critters, sorry to say.

I believe you are supposed to use OpenXR interface for MSFS in VR. This should work by setting SteamVR as an OpenXR “provider” in the SteamVR Settings.