ما صحة حديث جلوس النبي بجوار الله على عرشه، وما معناه؟

There is no prophetic hadith with this meaning. However, it was narrated from Mujahid regarding the interpretation of the verse, "It may be that your Lord will raise you to a praised station" that He will seat him on the Throne, but this is a weak narration. The Praised Station (Al-Maqam Al-Mahmud) is the Prophet's intercession for his community.