I changed emission shape back to point,
and then under 'Materials' tab, I created a 'NewCanvasItemMaterial'.
Then changed emission shape to sphere, and converted the material to 'ShaderMaterial'.
Did I do it correctly?
I see there is a script attached this time, but when I open it there are only two lines of code, which are
shadertype canvasitem;
rendermode blendmix;
I don't see 'emission shape uniform'. Did I go wrong somewhere?