Works great!

I have YoastSEO which is supposed to do this, but it doesn’t work.

Apparently that’s a known problem with it.

This plugin picks up the slack where YoastSEO fails! After installing and testing it, any new post I create has the stop words properly removed from the slug.

Works great alongside YoastSEO. No conflicts. Didn’t even need to turn off Yoast’s stop words filter.