There’s the presence enabled admin setting if you’d like to turn it off completely?
After a little exploration, I believe you can use a touch of CSS to target hiding it for a specific category. I’ve only given it a brief test, but it seems to work as expected (replace SLUG for the slug of your category):
body.category-SLUG div.presence-users {
display: none;
}
As it’s CSS, it can be ‘unhidden’ using safe mode or the browser inspector, but may be enough for your use-case?