I can’t find the autofill check box in armor paint any more. It used to be at the top. Has it been removed or replaced?
I don’t know, but maybe try right-clicking on stuff. Last time I couldn’t find something after the update it was in a context menu I didn’t know existed.
I finally found it. If you right click on a material, you can select “To fill layer” which creates a layer that automatically mirrors your material, and fills it on the whole object.