There's a new demo up now. You can install it from the Steam store page now by clicking Play Demo. The demo up previously was almost two years old (October 2019), because it was built right before the art revamp started. Consequently, this new demo has all-new art, as well as a lot of other changes. New music, new features, bug fixes, and some new content. The demo is about 1-2 hours long, depending on your playstyle, and ends immediately after the Dead Plains boss fight. If you're in the closed beta, there's a new build available for that, too. That beta version has close to an hour worth of extra content beyond what's in the demo.