Is it permissible for someone in a state of major ritual impurity (junub) to recite Surat Al-Fatiha for the purpose of ruqyah (exorcism/healing through Quranic recitation), especially given the presence of symptoms of jinn possession or sorcery and suffering from obsessive thoughts about ritual purity?

The basic principle is that janabah (definition) (ritual impurity requiring ghusl (definition)) prevents the recitation of the Quran. However, an exception is made for reciting some short surahs like Al-Fatiha, Al-Mu'awwidhat (Surahs Al-Falaq and An-Nas), and Ayat Al-Kursi, for ruqyah (definition) (exorcism/healing through prayer) or seeking refuge [with Allah], and similar purposes.

Ghusl (ritual bath) is not obligatory merely due to imaginations or doubt. Rather, it becomes obligatory when its cause is actualized. If something occurs that necessitates ghusl, it is sufficient to pour water over the body in any manner, and this only takes a few minutes. One must be wary of giving in to obsessive thoughts (waswas), as they can lead to great harm. It is advised to seek Allah's help and make abundant supplications to get rid of these obsessive thoughts and imaginations.