Have engines refuted any established openings?

Before engines, we already had many well-established openings that were utilized by top players. For example, the Ruy Lopez/Spanish Game has been around for centuries and is still very popular today at top-level play.

I am wondering, are there any openings that were popular pre-20th century that have since been refuted (and thus are seldom played today) by engines? 

Generally very dubious gambits for the most part, though they often would already have had some human-made refutation to begin with and the engine is basically just confirming it or finding improvements. The Colorado Gambit (1. e4 Nc6 2. Nf3 f5) is dubious, but some of the ideas that engines see for refuting it are very creative (for example 1. e4 Nc6 2. Nf3 f5 3. exf5 d5 4. d4 Bxf5 5. Bb5 e6 6. Ne5 Ne7 7. Ba4 is a fascinating novelty that has yet to be played with the idea of a cool positional sacrifice. If now, 7. ... a6 then 8. Nc3 b5 9. Nxb5 axb5 10. Bxb5 and the engine really likes this position for White, giving more than a +2 advantage)

Kings Gambit.

Can the king’s gambit actually be considered refuted? 

Here in the modern variation white barely hangs on to equality, but equal is equal. I’ve checked a lot of other lines and it seems white will always have a move resulting in an equal, yet sharp, game.

Alright, shoot for the KG and run into blacks multiple strong responses which is the least of your worries because there are the Sicilian, French, CK and other countries that will test you.

Enjoy because equality is your thing. I would rather avoid trick or treats year around.

The King's Gambit has not been refuted. It's very interesting to watch strong engines play it against each other. Top level grandmasters don't play it in classical (mainly because it's a very risky opening and they usually want to play it safe (i.e. be able to walk away with a draw in the worst case scenario)), but it does show up in faster time controls. GM Ian Nepomniachtchi has even released a Chessable course where he has used an engine to find some new ideas in this opening.

No no, Fischer already found this spending years on it - the King's gambit cannot be refuted.
Ivanchuk and Giri for example, have recently still played this at the highest level.

But yes, many openings have been refuted. The Englund is probably a notable one since people are still going for that stuff.

Why are you defending the KG when you don’t even play it?

Yes, the engine AlphaZero has refuted
Dutch Defence, Chigorin Defence, Alekhine's Defence, and King's Gambit, see Figure 4
https://arxiv.org/pdf/2009.04374.pdf 

Because you can know things about openings that you don't play. None of the facts that I stated (such as Nepo having released a course on it) actually require that I play it myself. I might play the King's Gambit in the future, but it requires a lot of study and there are other openings that currently have my attention.

Let’s be honest and cut to the chase, you don’t plan on playing the Kings Gambit ever?

You had no intentions.

You always say odd things.

Drawing >70% of the games is not a refutation.

Pre 20th century is 1800s so...

I guess you mean to say since mid 20th century... nothing has been refuted, but for example you don't see the king's indian defense at the top level anymore (Fischer and Kasparov played it).

And in general... it used to be that professional white repertoires aimed at getting an advantage out of the opening. These days everyone has access to the same technology and everyone can see that everything leads to an equal position, so the approach is very different... mostly white wants a position that isn't completely dead.

@12
"Drawing >70% of the games is not a refutation."
++ Losing 20% of games is a refutation. Normal is 88.2% draws (Figure 2).

A refutation is losing 100% of games.

@15

"A refutation is losing 100% of games."
++ At unlimited time. Figure 4 only used 1 s/move.

Feel free to publish your refutation of the King's Gambit.

You will become a Chess celebrity instantly.

@17
Fischer did that
http://brooklyn64.com/wp-content/uploads/2015/11/a-bust-to-the-kings-gambit.pdf 

I could not care less on arguing openings (a trivial topic) and the influence of engines but unfortunately this guy name Bobby isn’t around no more to rebuttal so I’ll just take his word for it. He may have written a book or two.

Why so hostile? There’s no reason for you to be antagonistic. Besides, this thread is supposed to be about engine refutations. Fischer’s “A Bust to the King’s Gambit” was most certainly written without consulting an engine, therefore it is irrelevant here.