What are these spheres at bottom-right in 3d viewport? I downloaded a *.blend file and open it.
I saw two strange spheres at bottom-right in 3d viewport.
What's this and how can I turn it on/off?
The spheres are called HDRI Preview spheres, in older Blender versions known as Look Dev HDRI spheres. You can turn them on/off in the overlay menu. It is used to check the lighting setup of an HDRI.