By default, Photoshop shows the contents of the sample point in the brush’s circle that you’re about to clone
This is incredibly useful if you’re cloning edges or objects, as it allows you to line up the results.
But it can get in the way for things like spot removal, because you need to see what’s under it.
To turn the preview off, click the ‘Toggle the Clone Source panel’ icon next to the blend mode box at the top of Photoshop.
In the floating palette, and at the bottom, remove the tick from Show Overlay. This reveals what’s under the brush.