You can find the raw data here though (Tables II: distributional series, you're looking for tab TG2b): http://gabriel-zucman.eu/usdina/
And then you can see that the highest effective income tax rate ever paid by the top 1% was 23.4% in 2001. The most current number from that table was 2019 when it was 20.3%. Whereas the highest rate from the mid-20th century period when they were alleged to have been paying such high income tax rates was 21% in 1945. In 1953, when the US had its highest marginal tax rates (92%), the effective income tax rate on the top 1% was 14%. Which is more typical for the period; 1945 was an outlier, it being the height of WWII.
The thing that has actually come down is not effective income tax rates on the top 1%, it's corporate income tax, which is a consequence of globalization. "Corporate income tax" is not a good fit for an international supply chain because tax avoidance and jurisdiction shopping is too easy if you're trying to tax something that only exists in a spreadsheet ("corporate profit") instead of something that has a definable physical location (goods, workers, real estate, etc.) So corporate tax avoidance is higher (because of transfer pricing etc.) and corporate rates are lower because it's easier for corporations to set up shop somewhere else if the somewhere else is taxing them less, which puts tax jurisdictions in competition with each other. But that's not an easy one to fix without abandoning globalization, so other taxes got raised to compensate (which brings us back to, government receipts as a percent of GDP haven't really changed).