What is the viscous, clear, yellowish fluid that is discharged after performing ghusl following menstruation, and what is the ruling on performing ghusl from it, especially if it sometimes comes out white with the same characteristics?

It is not obligatory to delay the ghusl (ritual bath) to ensure purity. The most authoritative opinion is that it is obligatory to hasten to perform ghusl immediately upon seeing purity. Yellowish or brownish discharges are considered menstruation if they occur within the customary period or are connected to blood. However, if this yellowish discharge occurs after the customary period has ended, then ghusl is not required of you. The white discharge is vaginal fluid, which is pure but nullifies wudu (ablution). These discharges originate from the birth canal, not the urinary tract.