The category could potentially be set as miscellaneous to avoid the user being shown too many categories if that's the main issue in adding it
You are probably reaching FPS above 150. When that happens on 1.27 the game bugs out and you get stutters. To avoid that you shall install RivaTuner Statistics Server.
Guide on how to set it up : https://www.speedrun.com/gtav/guide/wvnm7#ch3_FPS_Capping
This is a serie that is still in-making for every segment of the game. It is for PC, so there are some strats which are harder on console, but still a good start.
To downgrade your game to patch 1.27, there is a handy tool called "Project 1.27", you can install it here : https://github.com/TwosHusbandS/Project-127/raw/master/Installer/Project_127_Installer_Latest.exe
Yeah of course, why would it matter ? You have to provide a recording when you do submit your run though, so make sure to start recording when you start getting good times