Shaders and Polygons
One of the hardest things for the Quest to handle is transparency, you’ll notice that none of the shaders you can upload for Avatars even ALLOW it.
For worlds, most if not all the shaders included with Unity will function, though keep in mind that some custom shaders may not work correctly if not verified by their creator.
Single layer transparency on its own is typically no worry, where the Quest struggles is with OVERLAPPING transparency.
For worlds, this is most commonly found with foliage and window glass.
Another big restriction for worlds is that Post Processing, just like, as a feature, does not exist.
The visual effect is deemed too intensive for the quest to handle, so while it may LOOK like you can use it while testing in Unity, know that the effect will not exist when you’re in-game on Quest.
Polygon count is another big one, obviously the rule is “more is worse”, but they have specific recommendations for worlds aiming at around 50,000, and strict rankings for avatars aiming at 10-15,000.
A Quest avatar fallback NEEDS to be ranked Good or higher, which requires no more than 10,000 polygons.