You're referring to the classic 1981 film "The Great Muppet Caper" and its availability on the Internet Archive!

Directed by Jim Henson himself, The Great Muppet Caper was the second theatrical release for the Muppets. Unlike its predecessor, The Muppet Movie , which was a road trip film, Caper took the form of a classic British "whodunnit" musical.

Here's an informative report:

The serves as a digital library, preserving millions of pieces of media that might otherwise fall through the cracks of corporate licensing. When users search for "The Great Muppet Caper" on the platform, they aren’t just looking for a movie; they are often looking for ephemera that isn't available on mainstream streaming platforms like Disney+. What Can You Find There?

Lena double-clicked. Grainy 35mm sprang to life.

Lena paused the video. Her heart raced. She knew that badge. It was a prototype for the Jim Henson Legacy Collection—a rumored vault of “alternate emotional cuts” meant to test darker, more vulnerable Muppet stories that were never released.