We need to see the entire interface so we can see the document color and bitdepth, along with the layers panel, its settings and the brush settings. You probably have an incorrect blend mode set for the brush or layer. Make sure the blend mode is set to "Normal"
Thank you so much. When I changed to the standard mode, the brush became clean. I thought it was broken because the picture was too large. I posted a question after much consideration, and thank you so much for your kind answer. Everyone, have a good day!!!