Currently VR/XR is not supported, because the HNS canvas runs in screen space. We're already working on an addon for HNS, which already supports most of the features of HNS. A working beta will be released to the store once we've integrated all features of the main asset. Stay tuned!
2D is not supported "out-of-the-box", but we have a few customers, which successfully use HNS in their 2D/2.5D games. This mostly depends on the individual setup of your project. Please contact us for further advice, before you purchase HNS.
It should be self-explanatory, but we can't provide everyone with free copies of our addons :) We have only a handful of free vouchers available each year, so we exclusively give them out to students (with legal documents / proof of study).
That's actually really easy to accomplish with the Scene Manager. Just make sure you've enabled the Don't Destroy On Load setting on the HUD Navigation System and let the scene manager do the rest. For e.g. menu scenes, where you don't need HNS, simply disable the system on these scenes with the Disabled In Scene option.