Im planing on trying a %100 completion speedrun. Who can i contact to open a new category.

You'll need a definition for 100% and a run before a category is added but talk to one of the moderators after that. The closest thing that's been done is a Japanese all social links run.

How can i contact a moderator?(Im a bit new here Xd). And i mean by %100 all social links all ellizabeth quest complete persona compadium.

Id say 100% is max social links, all quests, 100% compendium, and max level (minus sweet bad boy).

There's a link to the SMT/Persona speedrunning Discord in the Megami Tensei series page.

As for the definition would absolutely require full compendium, all requests and completion of the Vision Quest. If there is some equipment that cannot be sold and carries to NG+ would probably require them as well. MC's level and money do carry over but requiring max money would be a weird requirement. I'd also heavily argue that it should done on either normal or maniac so that the fights would require at least some strategy.