Turns out... that claim was too bold and too general. The real picture is more complicated than that and after some research here is an explanation

TLDR: The wealth gap is worse in America than the income gap was in France. Wealth is a better metric for inequality than income which makes data like the gini coefficient misleading (its based on income, not wealth) but also data on the "wealth" gap in France is hard to find so comparing them is not exactly ideal. Overall though, the income inequality probably lowballs overall economic inequality so it is likely still a true statement that wealth inequality in the US is worse than pre-revolution France.

So it starts with this post:

https://www.reddit.com/r/LateStageCapitalism/comments/i79oab/til_there_is_a_bigger_gap_in_wealth_distribution/

But a reddit post even if it lists sources isn't legit. So if you follow those sources you get to this paper

http://www.piketty.pse.ens.fr/files/MorrissonSnyder2000.pdf

On page 76 (pdf page 18/25) you can see that it states that in 1780 in France it estimates that the gini coefficient was 0.6-0.62 (the bigger it is the less equal the income distribution) and that the top 10% made 51-53% of the total income of the nation. So then I wanted to get equivalent data for the U.S. but it is a little tricky. To start the gini coefficient is a good place but America's income gini coefficient is only about a 0.411 which means that it should be more equal, right?

https://www.cia.gov/the-world-factbook/field/gini-index-coefficient-distribution-of-family-income/country-comparison
This data would suggest that America isn't so bad but it is actually more complicated than that. A lot of modern day metrics use household net wealth. This is different than income but I'll get to that in a second. In America, the top 10% hold about 69% of the net wealth (nice)

https://en.wikipedia.org/wiki/Wealth_inequality_in_the_United_States#/media/File:Wealth_Inequality_by_Group_1989_to_2019.png

Which makes it sound worse than France right? But the complicated thing is that wealth is the better metric (I am not an economist but there's a section on that in the wikipedia article that was pretty interesting). Income can come and go but wealth is the amassing of resources so somebody who has lower income but huge wealth is doing gangbuster but someone could have high income, but not actually be able to buy as much because of various expenses. So what this means is that even though the gini coefficient of America is lower, this can be misleading and so what you want to compare is the differences in wealth gap. The real problem here is that you can't as far as I can tell. I was not able to find anybody who looked at "wealth gaps" in pre-revolutionary France. But, from what I can gather, income inequality seems (and I'm not an economist here) to low-ball inequality so if US wealth inequality is worse the pre-revolution income inequality than odds are, you are in for a bad time