Hey! There is always more to say about a topic, but I have touched on this question in previous answers I've written for the sub. In the first, I tackle different narratives surrounding the coronation, and what role the pope might have played, if any. In the second, I address the evolving understanding of Rome and the imperial tradition in the late eighth century.

There is of course, always more to say, and someone may be along shortly with a more complete, direct answer to your question. In the meantime, I am happy to answer any follow-up questions or clarifications best I can.