What is the ruling on seeking supplication and intercession from the deceased at their grave, if the supplicant believes that the deceased hears them, citing as evidence the Prophet's addressing of the polytheists in the Qalib (well) on the day of Badr? And does this differ from the actions of the polytheists in the pre-Islamic era? And is this considered major shirk? And are there multiple opinions on this matter?

It is impermissible to seek supplication or intercession from the dead, especially at their graves. This is because it constitutes a reprehensible innovation (bid'ah) and a means leading to polytheism (shirk), and it may even escalate to major polytheism (shirk akbar). Intercession is to be sought from Allah alone, and it will occur on the Day of Resurrection for those whom Allah permits. The Companions would seek intercession through the living, but they did not seek intercession through the Prophet, peace and blessings be upon him, after his death. Scholars have unanimously agreed that the dead neither hear nor benefit others. Whatever has been reported regarding the hearing of the dead in some instances is either a specificity for the Prophet, peace and blessings be upon him, or an exception for which there is authentic evidence, and it does not serve as a basis for inferring the permissibility of seeking supplication or intercession from the dead.