This article contains major spoilers for The Great season 3Despite being loosely based on the reign of Catherine the Great of Russia, The Great is not quiet about its many historical inaccuracies, and the third season of the series is no different. Following a young woman named Catherine who marries the boorish Peter III and decides to take his throne, the show openly refers to itself as "an occasionally true" story. During The Great season 3 in particular, there are a few major events that did occur in real life, however, there are many more that were either entirely fictionalized or changed for the series.
https://screenrant.com/the-great-season-3-true-story-show-changes/