Can the Pope be fired?
No. The Code of Canon Law has no provision that allows a pope’s removal from office- for any reason, even poor health or psychological trauma. That’s because, according to church law, there is no higher authority than the pope: He “possesses supreme, full, immediate, and universal ordinary power in the Church, which he is always able to exercise freely.”
A pope may resign, but his resignation must be “made freely,” and Question: he doesn’t have to tender his resignation to any particular authority.
The last time that happened was in 1415, Pope Gregory XII.
Can the pope face prosecution under secular law?
No. The pope is immune from prosecution under the local laws of the Vatican. It’s also a principle of customary international law that heads of state enjoy immunity from prosecution. That includes the pope, who is both the head of the church and the head of Vatican City.