If you want to speedrun Game Builder Garage (and even if you don't want), you can join this Discord Server: https://discord.gg/y8b26sBKfD . There have leaderboards and a form to request a run. You can also talk about the game in general.

Thanks if you join it and have a nice day.

Hey look at this extremely useful thread that was built specifically for this purpose
https://www.speedrun.com/speedrunning/thread/hl23s/4