there is also another way to get what you want
using a Circle, there are parametric Shapes in VectorStyler
which offers some options via the Shape Panel
Menu > Panels > Shape Panel

here a video

When bucket filling just one yellow ring with a different colour, this ring becomes a separate item, which you can drag off and the item you 'filled' remains unchanged.

Now I got it, yes, this is the intended behavior, to create a new shape. This can be changed by enabling the "Remove Shapes" option in the context panel. If enabled, then the filled parts are removed from the original.

When bucket filling just one yellow ring with a different colour, this ring becomes a separate item, which you can drag off and the item you 'filled' remains unchanged.

In the attached picture, the yellow circles are one item
.
I coloured each yellow circle in the colours you see.
I was then able to move the yellow circles away from coloured circles, which are all separate items.

I did not want this, I wanted a single item with different colour circles

As you can see in the layers, all the circles I coloured have become separate items.

In the context panel, uncheck "Merge Styles", then it will fill the separate cells.

Same would have happened for concentric shape also, if used the same colors.