I know this is similar to this question but I'm not interested in suppressing 20th century tech to create 21st century steampunk, but in creating late 19th century steampunk with fantastic, Jules Verne-like tech, such as airships to the moon, submarines, time machines, all running on some combination of steam and other (probably fictional) power source(s). My premise is that this sort of world was the "original" timeline (if there is such a thing), history was accidentally changed by time travelers to create the world as it exists today, and another time traveler needs to change it back. Thanks.

But we do all run on steam

All (non-renewable) power plants are steam driven. Even nuclear power is a glorified steam engine. What we don't do so much any more is drive directly using the steam, it's now a stage removed from the effect. The steam drives the turbines to generate electricity that drives your machines. As soon as you swap to an electric car, that will run primarily on steam (until wind/solar takes over).

We streamlined it, we hid the pipes and the smoke, toned down the brass and the grease, but it's still all steam powered.

You can't do it.

The reason that technology doesn't exist is because the world just doesn't work like that - we just didn't know that during Jules Verne's time.

Change the timeline as much as you like, the laws of the universe don't change.

Vhs or Betamax? QWERTY or Dvorak? MP3 or WAV? HTML or some long-forgotten alternative? Should we drive on the left or right side of the road? How wide should train tracks be?

All of these are example of cases where two possible ideas came along at or near to the same time. Some people made one choice, others the opposite choice. For the first four examples, one of the two arrived just enough earlier, or had better advertising, or was able to saturate the market faster, or some other small factor, as to become the "better" standard in the eyes of the buying public, and therefore killed off the competitor. In some cases, one can argue the losing choice carries clear advantages, but not enough to overcome the tidal wave of momentum gained by the ultimate winner.

This is all you need. An inventor with right gumption and determination, coupled with charisma, foresight, and so on, who gets steam ready at just the right time, gets it in the eyes and hearts of the public quicker, and makes it essential to life as they knew it. Now, gasoline and electric can come along and tout itself to the stars, but people won't care- they already have that machine in a steam version, which is cheaper, easier to find parts and service, and works just fine, thank you.

Come to think of it, this is exactly the situation electric cars are having right now. The infrastructure around gasoline is everywhere, and is comparatively cheap. They probably will make it, but they will struggle as they have been for several more years before they do.

Antoine Lavoisier should not have been executed

Lavoisier's importance to science was expressed by Lagrange who
lamented the beheading by saying: "Il ne leur a fallu qu’un moment
pour faire tomber cette tête, et cent années peut-être ne suffiront
pas pour en reproduire une semblable." ("It took them only an instant
to cut off this head, and one hundred years might not suffice to
reproduce its like.")

While Lavoisier is known as one of the greatest scientists of his time, he was also a philanthropist and, more importantly, a competent administrator. Before the Revolution, he had been the manager of the Gunpowder Commission, and an excellent one at that. Anecdotally, he appears to have been of a great help to the founder of the DuPont company.

Alas, he was basically framed for the terrible agricultural policies of the government under the Terror, which made him a convenient scapegoat and gave a pretext for confiscating his fortune. He was summarily convicted with ballooned charges and executed.

And yes, I am still bitter about it.

Now, had he survived the Terror and made it to the quite scientist- and engineer-friendly Napoleonic regime, you can have him develop technologies early. The obvious ones are high-grade steel (that is, more modern blast furnaces) for high-pressure steam engine, smokeless powder/solid rocket propellant and rocketry, or let's be crazy pulsejets and later even maybe ramjets. He had already invented a way to produce hydrogen, and hydrogen balloons were becoming a thing, and he may further pursue the idea as well.

Avoid anything having to do with electricity, though - you want those technologies not developed early for steampunk to work. Ideally, you want them to take a backseat because other early tech are prioritized. So you can have rocket/ramjet supersonic planes without electricity, if you want.

Time travel is a bit harder to place on the tech tree, so you will have to use some handwave there.

A side-effect may be, even with a small technological edge, that Napoleon ultimately wins, or at least ends up with enough strength to impose an advantageous status quo. The Indian subcontinent will be very happy, Spain not so much. Geopolitical consequences are beyond the scope of the question, but at least this would change from the ubiquitous Steampunk British Empire.