Press "H" to hide/show variables, and press the green flag to generate. View on Turbowarp for much faster loading: https://turbowarp.org/1280156088 If you view it on Turbowarp you have to press "see inside" if you want the progress display to work.
This is my entry for the 2nd Technical Scratcher Scratch-Off. The settings that produce the best terrain (in my opinion) are resolution at 10, smoothing at around 100, variation at around 20-30, mode on vegetated land 2, and water level at around 5-8. It's a really basic concept, so I'm honestly surprised it worked. Basically, it starts with a grid of pixels pixels that each are assigned random value, and then, for every pixel, sets its value to the average of the values of the pixel above it, the pixel below it, the pixel to its right, and the pixel to its left. Then, it colors each pixel based on its value. And if it colors the pixels in the right way, you can get images that look like terrain, like in the "vegetated land" mode or the "mountains" mode or the "desert" mode. Update (as of Feb. 17): Optimized code, shaved off 74 blocks.