I recently did a speedrun of Software Inc and I noticed that the game is not available, what should I do in terms of the run itself. Also, if it is approved, who would decide the categories, me or someone else?

..slowly but surely I wonder if people actually try to look for the answer before asking (seeing how there's been at least 4 of these in the past 2 days)

https://www.speedrun.com/requestgame request it there - you'd become the moderator of the game - in essence, you'd create the categories. although you should in theory also listen to what other people want/need (if anyone else is running it).