Dandelion, DriveThruRPG quietly moved their old site design to legacy.drivethrurpg.com. The toggle to "Opt Out of the New DriveThruRPG" in Account Settings is a misleading McGuffin that doesn't actually do anything.
So for now, I can still use the old site design instead of the horrendous mobile-first redesign, with all its fiddly little "swipe left" wheels that just don't work on PC browser.