What is the ruling on the fluid that exits the penis upon light squeezing after sleep, or after eating a lot, or after physical activity, when it is between the characteristics of madhiy and wadiy? And is it treated the same as madhiy and wadiy in terms of the necessity of washing the garment?

As long as the fluid emanating from either of the two private parts is not semen, it is impure. This is because the default ruling for any fluid exiting the private parts is impurity, and it is treated like urine. It is not necessary to wash all undergarments; it is sufficient to wash only the part that has been soiled. One can protect against this by taking measures to shield the clothes. If there is uncertainty whether it is semen or not, you have the choice to consider it semen and perform a ritual bath (ghusl) for it, or not to consider it semen and wash what has stained your clothes.