Is this half wall with spindles load-bearing?

It's difficult to see exactly how this is framed, but...The 2x framing directly below your blue line appears to be the top plate of the wall with spindles in it. That wall appears to be supporting attic/ceiling framing members. The perpendicular members (2x6?) appear to be bearing on the spindle wall, and not spanning over. That leads me to believe that the spindles cannot be removed, without some means of reinforcing.

With some additional information you might be able to tell how best to make it work. You might be able to replace the spindle wall with a beam in the attic space, spanning from the 2x12 beam to the next load bearing wall at the other end of the spindle wall. You could possibly use joist hangers to frame the perpendicular 2x6 members into the face of the new beam. All of this would need to be designed for the appropriate loads. That is just conceptually how I would approach it. But it really is necessary to get a better view of the framing. Too much is concealed by insulation, to make a confident judgement.

In my experience spindles such as that have never been used in load-bearing situations by legitimate builders. Doing so would create two hinge points along the wall's height, which would be plain dangerous.

Given that fact, the arrangement and location of the wall, and the attic situation, I'm reasonably confident that the wall isn't structural.

Should you make decisions based on that? Nope. Get someone on site.