What is the ruling regarding performing Friday Prayer behind an imam when there is an obstruction that prevents seeing him and the connection of the rows? And if it is invalid, should it be repeated as Dhuhr or as Jumu'ah?

The correct view is that the Friday prayer is valid for someone who prays outside the mosque if they hear the Imam's takbeer or see some of the congregants, even if the rows are not connected. Accordingly, your prayer in the front building is sufficient, and you are not required to repeat it if you hear the Imam's takbeer or see some of the congregants. As for someone who misses the Friday prayer or whose prayer becomes invalid, they must pray Dhuhr instead.