If you guessed "X-Plane 11.00 public beta four", you are right. 🙁 I screwed up the shaders, and they work on AMD cards and OS X but not NVidia cards.
So: public beta three is the official public beta again, and we'll have a new public beta five out tonight that will fix this.
If you got the broken beta four (in the hour it was out before we caught this) you can re-run the updater by hand and force yourself back to beta 3, or just wait for beta 5 and then let auto-update do its thing. Unfortunately there's no work-around in-app.
This one is definitely a big omelette on my face; I regularly swap through all of the major driver stacks on my PC and Mac to try to make sure the shaders work everywhere. In this case, I had "one little last change" that I only tested in some places, and sure enough, it looked innocent, but failed only on the configs I hadn't tested.
Update: beta 5 is out and works on NVidia Hardware - just run the sim and let it auto-update. Beta 5 does have interior cockpit flashing - until we fix this, you can set the reflection detail to its lowest setting to work around this.