TL/DR:

The only real doctrine in the LDS church is obey the current prophet no matter what else you have heard or what has been written.

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What God teaches is called doctrine. God supplies doctrine for His children by way of commandments and instructions that will bless them and bring them happiness. Just as He did in Old Testament times, God continues to reveal doctrine through prophet
https://www.churchofjesuschrist.org/media/video/2019-10-0150-what-is-doctrine?lang=eng

• Doctrine consists of fundamental, unchanging truths of the gospel of Jesus Christ.
• A principle is an enduring truth or rule that individuals can adopt to guide them in making decisions.
• Some doctrine and principles are stated clearly and overtly in the scripture text, while others are only implied.
  https://www.churchofjesuschrist.org/study/manual/new-teacher-training-resource/at-home-learning-experiences/learning-experience-7-identifying-doctrine-and-principles?lang=eng

Not every utterance by every general authority constitutes “official” doctrine. “There are many subjects,” we read in the First Presidency-authorized Encyclopedia of Mormonism, “about which the scriptures are not clear and about which the Church has made no official pronouncements. In such matters, one can find differences of opinion among Church members and leaders. Until the truth of these matters is made known by revelation, there is room for different levels of understanding and interpretation of unsettled issues.”14

https://www.churchofjesuschrist.org/si/questions/what-is-doctrine?lang=eng

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n all types of doctrine—whether core, supportive, policy, or esoteric—the Lord can always reveal more. We believe that God “will yet reveal many great and important things pertaining to the Kingdom of God” (Articles of Faith 1:9). This implies that new ideas, altered concepts, expanded teachings, and additional knowledge will be given, thus requiring doctrine to be flexible. This does not mean that some doctrines cannot be eternal or immovable, just that certain concepts have yet to be revealed and may alter as new perspectives are gained. The very notion of a living Church and continuing revelation suggest that most authorized teachings reflect current understanding and expediency, not eternal finality.
https://www.ldsliving.com/how-to-distinguish-doctrine-from-policy-why-there-is-more-than-one-type-of-church-doctrine/s/91274

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These same patterns are followed today in the restored Church of Jesus Christ. The President of the Church may announce or interpret doctrines based on revelation to him (see, for example, D&C 138). Doctrinal exposition may also come through the combined council of the First Presidency and Quorum of the Twelve Apostles (see, for example, Official Declaration 2). Council deliberations will often include a weighing of canonized scriptures, the teachings of Church leaders, and past practice. But in the end, just as in the New Testament Church, the objective is not simply consensus among council members but revelation from God. It is a process involving both reason and faith for obtaining the mind and will of the Lord.4

At the same time it should be remembered that not every statement made by a Church leader, past or present, necessarily constitutes doctrine. It is commonly understood in the Church that a statement made by one leader on a single occasion often represents a personal, though well-considered, opinion, not meant to be official or binding for the whole Church. The Prophet Joseph Smith taught that “a prophet [is] a prophet only when he [is] acting as such.”5 President Clark, quoted earlier, observed:
https://www.churchofjesuschrist.org/study/ensign/2013/09/how-is-doctrine-established?lang=eng

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Wednesday, 8. —This morning, I read German, and visited with a brother and sister from Michi- A Prophet not gan, who thought that a prophet is always a Always a prophet;" but I told them that a prophet was a prophet only when he was acting as such.
http://ia800606.us.archive.org/17/items/HistoryOfTheChurchOfJesusChristOfLatter-daySaints1902-Volume5_249/history_of_the_church_vol_5.pdf