Does the Friday Prayer become invalid by adding two non-obligatory prostrations before it? And what should the Imam and the congregants do after they disperse if the prayer is invalid?

The question is unclear, but reciting a Surah (definition) after Al-Fatiha is a Sunnah (definition), not an obligation or a pillar. If one intentionally omits it, no prostration of forgetfulness (Sujud (definition) Al-Sahw) is required. If the Imam prostrates before the Tasleem for omitting the Surah forgetfully, his prayer is valid. However, if a congregant (Ma'mum) prostrates, their prayer becomes invalid, unless they did so out of forgetfulness or ignorance of the ruling. If the Imam recites part of a Surah but does not complete it, and then prostrates for forgetfulness while knowing it is unnecessary, his prayer and the prayer of the congregants become invalid due to the invalidation of the congregational prayer, which is a condition for Friday prayer. And Allah knows best.