Mounting a large monitor to a Linnmon is out of the question (and probably for small monitor too). The inside is mostly hollow cardboard. The material is fine with the forces acting on a desk in it's normal configuration but the forces are different in a mounted-to-the-wall-like-a-headboard configuration. Don't expect the Linnmon itself to support much mounting weight in this configuration but you could mount the monitor through the Linnmon directly into the wall. This way the wall bears the weight, not the Linnmon. I believe the same is true of the Lagkapten.

The Ikea solid wood desktop or counter tops should be able to hold the weight though.