Gibbon didn't have access to the vast majority of the information he would have needed to say anything really useful about the Roman Empire. And Gibbon's analysis of the causes and factors that led to the fall of the Roman empire really wasn't in line with even the limited information he had.

Gibbon's analysis was highly motivated by promoting enlightenment values, and making people (possibly including himself) think historical analysis strongly backed them over traditional values in Europe at the time. The pose style was also groundbreaking and very influential from what I understand.

So if you're interested in the history of literature or the philosophy of the enlightenment it's a super interesting thing to read. But don't assume it's telling you anything useful about the history of the Roman empire, it definitely isn't.

Useful discussion, analysis, or interpretation of social structures, government structures, the economy, the military, demographics, religion, cultural changes etc. are just not in there at all. And Gibbon had essentially no access to archeological information of any kind.

So The Decline and Fall of The Roman Empire is a hugely important book, you can learn a ton from reading it. But almost none of the useful things you can learn are going to be about the Roman/Byzantine Empire and it's a big problem how many people read it and think they're learning about that.

And none of this is particularly casting shade on Gibbon. He brought together a ton of sources in a way rarely done before and tried to do a very detailed synthesis. Proper academic history was not a thing and he didn't do anything wrong.

Gibbon to a pretty large extent was trying to analyze the past as part of a project of making sense of the past and the present. It's a book about 18th century Europe and the conflict between traditional society and the enlightenment and nothing about it makes sense outside of that context.