Is it permissible to perform the Friday prayer and deliver the sermon in the streets, at the closest barrier to Al-Aqsa Mosque, in the event of being prevented from entering it?

Friday prayer is valid in the desert near buildings and roads, but not in areas far from them. Your prayers are valid, especially if you were prevented from praying in the mosque and could not follow its Imam. However, if you are able to follow him, then you must do so, because praying independently when it is possible to follow would lead to an unnecessary multiplication of Friday prayers.