How to be more approachable at work?

When I'm at work I'm usually on my laptop/at a table working. I usually just look locked in and busy even when I'm doing nothing, just so it doesn't look like I'm doing nothing.

But at the same time, I also want to be approachable for people to come talk to me. I'm not someone who goes out of their way to talk to people first (unless it's someone I really do want to talk to and basically have to be the initiator since they won't be that for me), so if someone comes over to chat with me, I'm more than happy to talk to them since they went out of their way to approach me.

So how can I become more approachable to other people for someone who is introverted but at the same time is more than happy to chat with people who take the time to initiate the discussion with them first.

Even the way I sit at my table, I try doing so in a way where I'm not just hunched over the table staring at the screen, I'll be a bit more laid back or just sitting upright.

And sometimes coworkers I have need help getting in or out of a certain door (you need your badge to get through), and even if I'm right there and all they have to do is ask, 99% of the time people will rather just stand at the door and hope their friend or peer sees the from the other side and just opens it for them. Meanwhile I'm sitting there happy to help when called upon. Maybe they just think they're bothering me even though any time someone has ever asked me for help I'm happy to help.