Adventist’s will often try and boil this entire narrative and it’s doctrines down to a very barebones claim that it’s simply the belief that Satan is working against God to then point to scriptures that say such. This is not only dishonest, but incorrect.
The way that Ellen G. White functions is their church is they believe she adds inspired details to the biblical text that aren’t found in the Bible. And that’s precisely what the Great Controversy is. It is a bunch of extra biblical details read into the Bible that originated from Ellen G. White (though they will claim God ultimately revealed these things to her). Adventist scholarship is on record stating exactly this—that the Great Controversy was not something they discovered, but something they were uniquely given by God through Ellen White.