Is the non-transparent white fluid that is discharged after urination, and whose exit is felt as drops heavier than urine, considered maniyy (sperm/seminal fluid) or wadiyy (thick, white fluid discharged after urination)? And if it is maniyy, does it necessitate ghusl (ritual bath), or does it not affect fasting and the performance of obligatory acts like reciting the Quran and praying?

The fluid that exits after urination is called wadi, and it is impure (najis). It necessitates istinja' (washing the private parts) and washing whatever part of the body and clothes it has stained. It also necessitates wudu' (ablution). However, it has no effect on the validity of the fast or other acts of worship.

As for semen (mani), it does not invalidate the fast in all cases. Its emission without desire is a matter of scholarly disagreement regarding whether it necessitates ghusl (ritual bath).