So, I would like to see the Roblox game Sonic Simulator be added to speedrun.com. I have made a speedrun of the game. Basically, there's a track you run through, and aim for the fastest time. I can link my video:

What exactly is your question?

If you ask how to request a game for the site, it can be done here: https://www.speedrun.com/requestgame If you ask if the game will be accepted, then high chance it would not, because it is extremely short per the game request rules.

Actually the Roblox series has plenty of different gamemodes here on src, and when I checked one at random, the WR was 43s. So I think this would have its place in there

It looks like the ROBLOX community has their own game submission page located here.