Previously I have mentioned the works by Norman Gulley, and his second, 676 page volume II on the Trinity. In addition other volumes in that set have information on the Trinity.
An additional work on the Trinity is in Volume 12 of the Commentary Reference Series, Handbook of Seventh-Day Adventist Theology, 2000, 1,025 pages. A major article in this book is the 54 page article, “Doctrine of God,” by Fernando L. Canale. In addition, other articles may have something to say on this subject.
In all cases, what people say in their books and articles are important individual opinions, but, may not be fully in accord with the voted statements of SDA belief.
I do not personally know either Norman Gulley, or Fernando Canale. I perceive Canale as being a bit on the conservative side of Adventism, and Gulley is resident as a SDA University that is considered to be on the conservative side of Adventism.
Often times when people discuss somewhat esoteric subjects, their failure to fully communicate is due to differences in understanding important words that each is using. For that reason, I intend to comment on issues in a manner that sets out how some important words are understood in the hope that better communication can take police. Those words will be bolded.
NOTE: It should be noted that when I cite another person, unless I provide quotation marks, I have stated that person in my words and I am not making an exact quote.
Timeless: There is a view that God is eternal and beyond time. As developed by Parmenides (540-470 BCE) he stated that God was timeless. This view was accepted into Christian theology by some theologians who stated that God is timeless. As I understand this, a primary reason for accepting this view is the idea that God is eternal and to say that God is not timeless would be a denial of the eternity of God.
Seventh-day Adventist theologians have tended to deny the idea that God is timeless. This is not due to the idea that God is not eternal, as they accept the eternity of God. Rather it is due to the idea that God has often interacted with humanity in time. The incarnation took place in a moment of time. Individuals may enter a salvific state at a moment of time. These ideas are expanded into other reasons.
In short, on this subject, miscommunication can occur. But an accurate understanding of how each side is using the term may demonstrate that the differences are not as large as has been thought.
Immutability: “The Immutability of God is an attribute that ‘God is unchanging in his character, will, and covenant promises.’ “ (https://slife.org/immutability/) Seventh-day Adventists would not have a problem with that definition. As Canale has said: “. . . God does not vary, nor does He change from a less perfect into a more perfect being. God is always the same.” As Canale also said: “” . . . the Bible conceives divine change in relation to God’s dynamic life, and not in relation to the constitution of His being.”
Impassibility: “The impassibility of God deals with whether or not God can be emotionally affected, either externally or internally by something or someone other than himself. It also concerns the relationship between God and people regarding our effect upon God as it relates to his emotions. Can God thus experience pain and suffering due to our sin? How is he affected by our actions? Does he react to us? It is a complicated topic. The doctrine of impassibility has slightly varying views.” (https://carm.org/about-god/what-is-the-impassibility-of-god/)
The critical issue here is whether or not God is controlled by what God sees happening in human life. Love is an emotion. Does God experience love? SDAs would say that God experiences love for humanity and that this is evident from the salvation provide by Christi on the cross.
But, God’s emotion of love does not change God’s activity toward humanity. In the final end of time, God will accept the decision of some people to not be given the gift of spending an eternity with God. GOD’s love allows repentant people to be given such a gift. It does not result in God forcing people to spend such an eternity with God that they have chosen not to accept.
I hope that this gives some understanding of the alleged differences that SDAs may be thought to have.