Type in a seed with only numbers or else it won't work. Best results are with with 3 digit seeds; max number that i found that gave good results is 7000. However, it's random so results aren't guaranteed. Try any seed you want! Also, make sure turn on turbo mode (Shift + Green Flag) Seeds close to 100 may give results similar to the thumbnail. Seeds below or equal to 10, in my experience, haven't yielded any results.
Check out the other pen shenanigans! pen shenanigans 1: https://scratch.mit.edu/projects/1245211881/ pen shenanigans 2: https://scratch.mit.edu/projects/1267377496/