That's how it inevitably goes with Turing completeness :)
The real achievement here arguably isn't running code (that's provided by the PDF spec and implementations), but managing to hook it up to user input/output in an ergonomic-enough way to play Tetris.
Amazing, thank you!
The PDF [1] containing the Lambda calculus term manages to hang/glitch/crash both Firefox's and macOS Preview's PDF renderer, which in itself is quite the achievement in portability.
Update: Nevermind, Firefox handles it perfectly, it just (probably wisely) disables seamless scrolling and I have to use the "next/previous" page buttons manually. macOS got there after a minute or two of loading with no UI indications.
The mention of Turing Completeness got me curious, so I looked something up. Behold, a C compiler written in Lambda Calculus: https://github.com/woodrush/lambda-8cc