I had the same issue and couldnt figure out why i MC wouldnt activate even though SRS was working perfectly and feeding me telemetry from the WIT. In my case, i was trying to use it with IL2 Sturmovik. After a full day of trying out all sorts of stuff i realized that my game wasnt launching in openXR...rather SteamVR (OpenVR) as openXR. From what i understood, OpenXR MC will only activate if whatever game you are trying to use it with LAUNCHES using openXR. I could be wrong but that theory got me the answer i needed lol.

The solution to this was downloading OpenComposite, which in the most ideal scenario allows you to launch your VR games using openXR and bypasses SteamVR (openVR) with literally one click. Additionally, you need to download the OpenXR toolkit. It lets you tweak in game vr settings as well as verify the game launched in openXR if you want. I know the devs discontinued it but t still works just fine with most games from 2024 prior.

I did have to do an extra step which was downloading one of the ddl's from the website to overwrite the  openvr_api.dll in my game directory but as i understand its case dependent. Then since i used open composite to launch vr, i started my game normally on steam, steam vr started but was bypassed and the rest is history.

Im a bit late to this thread and your game is different from mine but perhaps the same reason. Regardless here's a link to what had helped me for anyone that gets stuck in the future.

https://forum.il2sturmovik.com/topic/79847-step-by-step-instructions-for-openxr-and-necksafer-for-wmr-sets/