Is what Al-Yamani mentioned in the book "Al-Ibadah" — that whoever embraces Islam and then commits major shirk out of ignorance, forgetfulness,, or error is excused — considered valid? And can the root of the religion remain in that state, as Al-Mu'allimi believes?

Shaykh Abd al-Rahman al-Mu’allimi is one of the great contemporary scholars, and his book "Lifting the Ambiguity from the Meaning of Worship and God, and Realizing the Meaning of Monotheism and Polytheism with God" is among his most important works. To understand the significance and standing of this book, one can refer to the introduction of its verified edition, which is available online. As for excusing a Muslim who falls into certain types of polytheism due to ignorance or error, this matter has been detailed in previous fatwas.