I've noticed a lot more movies about the horrors of Nazis in WWII than the horrors of slavery in America. There aren't zero movies about the latter, but there are much fewer than one would expect.

This strikes me as strange. I presume you ask why, and I will presume to answer.

As a nation, Germany started in 1871. Nazi Germany existed from 1933 to 1945. That's about 12 years of its 150-year existence or 8% of the total time.

Let's put America's starting point at 1776, with the Declaration of Independence. Slavery existed from its beginning until the Thirteenth Amendment got passed in 1865. Slavery was legal for 89 of America's 245 years or 36% of the total time. That's over four times as long as Nazi Germany was in power.

But one could argue that percentage is too small. We could also consider the following:

Best-case scenario, America's slavery lasted over four times longer than Nazi Germany. Worst-case scenario, it was over 20 times longer.

If that's not enough, here's one detail not included in many of those Nazi-era movies.

Before and after slavery was illegal in America, Americans had lynching postcards. They would kill Black Americans, then smile and pose with them in the background. They'd send those photos to their family with happy messages. As far as I've found, German citizens weren't sending postcards poses with the ashes of dead Jews rising in the background.

That one still stings, no matter what the "correct" math is.