Tested on Oculus Go (with touchpad) and VR BOX2 (with joystick).
For tests on a desktop (Windows 10 + Chrome) the "inline" webxr session and
A,S,D,W,↑,↓ keys for navigation are used.
For particle sprites one can use point primitives or
billboards. Points are simple and efficient.
Unfortunately, orientation of the points is tied to screen,
so they rotate with the screen if you tilt your head left or right.