If I put the Apple Watch Series 5 on my lanyard would it still be able to count steps and activity?

Counting steps depends on your arm swinging forward and back, creating acceleration and deceleration events. In your pocket or on a lanyard is not going to do that unless you walk forward 2 steps, and back 1, forward 2, back 1, or you lean forward, lean backwards while walking.

Yes some steps might get counted, when you start/stop and change direction, but most of the movement will go unrecorded.

Of course it will not measure your heart rate so it will not give you any credit for exercise.

Basically, it will not be very effective while at work.

Wear the watch on your ankle,I personaly know 3 nurses in a hospital that do this very successfully.

Or this;