that is all

I see people put it in their OP, if the specific section allows editing of the OP for the life of the thread.
Others have put their online status in their forum signature.

It's in all honestly, a bad practice for the general public.
People would leave their status as online by accident and on purpose.

Site suggestions

Try here - https://forums.d2jsp.org/forum.php?f=258

No i mean lets say you are in the trade forum for idk d2r then you click a button and it filters out the ops that arent online at that moment

I'm logged into d2jsp 24/7
even while sleeping.

My point is still valid.

Simple after x amount of time of inactivity it toggles you offline

Click on any user's profile and you can see.

Last Seen
# seconds/Minutes/Hours/Days ago

You are missing the point entirely. When trading clicking every thread of people who are offline is time consuming if you can toggle to not show threads where the OP is not online it would save massive amounts of time.

You can also try PMing a user, they will receive a notification.

If they have it setup it will even alert their phone.