Is delivering sermons after burying the deceased, concluding them with a collective supplication at the grave and a unified "Amen," considered part of the Sunnah and Islamic law?

Reminding people of death and what comes after it when burying the deceased is legislated and praiseworthy, for the Prophet, peace and blessings be upon him, did it when he sat by a grave that had not yet been dug, and he delivered an admonition about the state of the believer and the disbeliever at the time of death.

After the burial is complete, it is legislated for those present to stand by the grave and seek forgiveness for the deceased and supplicate for his steadfastness. The Prophet, peace and blessings be upon him, when he finished burying the deceased, would stand by the grave and say: "Seek forgiveness for your brother and ask for steadfastness for him, for he is now being questioned." Ibn Taymiyyah inferred from the verse in Surah At-Tawbah (9:84), "And do not pray over any of them who dies ever, nor stand over his grave," that a believer is prayed over before burial and one stands by his grave after burial.

However, one must limit oneself to what is legislated and authentically transmitted, for supplication is an act of worship based on divine revelation. Group supplication and collective "Ameen" after burying the deceased are innovated acts, because they were not from the guidance of the Prophet, peace and blessings be upon him, nor from the guidance of his companions. Therefore, a Muslim should adhere to what is authentically transmitted, for in it there is sufficiency and safety from innovations.