I saw videos about it and most of them are interesting and uses a lot of efforts. is slowrunning allowed? Would it? Can we make a slowrun category at games?

Slowrunning is boring and unfunny imo. You can do whatever you want, but moderators are not required to verify your runs if you are intentionally going slow.

the only situation i can think of where "slowrunning" could be interesting is in like a racing game. having to finish first against the cpu drivers but still having the worst possible time and you wouldnt want to drive too far ahead the cpu because of rubber banding making them faster. but again itll probably be interesting only in theory though and really hard.

and i yes i personally will reject someones run submission if its clear their intention isnt to beat the game with the intent of going fast

I guess you are free to do whatever you want.