1. Is it valid to say, "Peace be upon the Prophet" instead of "Peace be upon you, O Prophet" in the Tashahhud? 2. Are both formulas, "O Allah, bless and grant peace to Muhammad and to the family of Muhammad, and grant blessing and peace to Muhammad and to the family of Muhammad, as You have blessed, granted peace, and granted blessing to Abraham and to the family of Abraham, indeed You are Praiseworthy, Glorious," and "O Allah, bless and grant peace to Muhammad and to the family of Muhammad," valid for sending blessings upon the Prophet both inside and outside of prayer? 3. Is the prayer of one who restricts themselves to supplication in prostration, without saying "Glory be to my Lord, the Most High," valid, knowing that glorification is a pillar?

Regarding your first question about the wording of the tashahhud, the correct form for the worshipper to say is: "Peace be upon you, O Prophet, and the mercy of Allah and His blessings." This is because it is what is established in the hadiths. What was narrated from Ibn Mas'ud (may Allah be pleased with him) regarding changing the wording after the death of the Prophet, peace be upon him, even if it is authentic from him, is an ijtihad (independent reasoning) that does not contradict the established hadiths.

As for restricting oneself to du'a (supplication) in prostration without tasbih (glorification), whoever intentionally does so has abandoned a sunnah (prophetic tradition) of the prayer. Their prayer is valid according to the majority of scholars. However, Imam Ahmad considers tasbih in bowing and prostration to be among the obligations of prayer, and intentionally omitting it necessitates the invalidation of the prayer. If it is omitted due to forgetfulness or oversight, then the prostration of forgetfulness (sujud as-sahw) is required. A Muslim should not intentionally abandon any of the sunan of prayer.