What technologies to use if you need to make versions for several platforms?

Question

Cross-platform

Good afternoon. For android, for SteamVR, for android oculus quest, for future XR formats (augmented reality glasses).

On what to program, where to store data, etc.

Answer 1

Unity

Answer 2

If this is a project of some kind of visualization, then probably yes, Unity is the easiest way - universal and relatively easy-to-enter.
If this is a pet project or it's not clear what, if only there was something - then choose JS :) You can now write the web on it, you can also create cross-platform applications. Both VR and AR can be done on it, and 3D / 2D can be drawn. In short, anything, more complicated of course than in Unity, but more universal. Maybe.
You can work with data anywhere. It depends on what specific data and how you need to work with them, then choose (there are also more than enough systems)