In order to rein in the ads and “Promoted” posts in your Twitter feed, you need to uncheck all of your “Interests” in the Ads preferences section of your Settings. This list is usually in the hundreds, if not thousands—and each item must be manually unchecked. ☹️
This script helps enormously: Automatically Unchecking Twitter Interests. I found changing the timer from “100” to “3000” was the sweet spot where it was working through these checkboxes in decent time, but not triggering a whole bunch of 500 errors or hanging up.