Do you have any external hardware (besides mouse and joystick) hooked up to X-Plane?
If so, disconnect it and see if that changes anything.
If not, A reinstall may be in order. Your airframe is saved in the Output/TBM900/state folder. So feel free to back up that entire folder and put it back in to the reinstall.
However, I'm almost certain this will reintroduce the problem. But feel free to try it.
In the meantime, we'll continue to look into this and see if we can reproduce.
The oxygen system that is displayed in the G1000 is for emergency oxygen only. It's delivered by the oxygen masks above each cockpit passenger. The cabin is automatically pressurized, and hypoxia will only occur with a ruptured cabin pressure vessel. When this happens, hypoxia will, indeed, start to come in.