What is the ruling on making up prayers missed for many years, given the presence of obsessive-compulsive thoughts related to ablution, impurities, and the opening takbeer (takbeerat al-ihram)?

The most prudent and safest approach is to make up for missed obligatory acts of worship or those that became invalid, and this is the view of the majority of scholars. As for one who follows a scholar whose knowledge and religiosity they trust, they have fulfilled their obligation and the burden of responsibility is lifted from them, for Allah Almighty says: "So ask the people of the message if you do not know." As for intrusive thoughts (waswas), they must be repelled and not given attention unless you are certain of a reason that necessitates invalidation. Doubt has no effect after the prayer has concluded. One should avoid causes of intrusive thoughts, adhere to practices that promote humility (khushu'), and frequently supplicate.