I have the MS store version of MSFS and am now using a Vive Pro 2.
When I was using the G2 I would start SteamVR which would also start the Mixed Reality Portal. Because SteamVR started then OVR Toolkit and fpsVR would also start.
So after making sure my VR was working then I would start MSFS from a desktop shortcut and once fully into the cockpit tell it to go into VR. At that point my OVR Tooklit windows would be available using the G2 controllers.
A small downside is you cannot tell the G2 controllers to not go to sleep like I can with my Index controllers. That is one of the many reasons I have moved on to my VP2.
Hope this helps you get your G2 working on SteamVR. Another issue I did see since SU5 is many many many dropped frames using the G2 with SteamVR. I found it common to drop 10000 frames in a 1 hour session while having a FPS or 45. Made no sense to me but have moved on,