How can I unlock the Z axis in Scene mode?

I am using this tutorial.

In Scene mode I am unable to move anything along the Z axis. I click it, and drag, but nothing happens, I can move anything along the X and Y axes just fine. Did I somehow lock the Z axis? Or is it because of the assets I am using blocking the Z axis?

Also, if I try editing the position manually, it won’t change.

I just would like everything on the same Z axis for ease of level creation.

Thank you very much.

Maybe you’re just viewing the scene in ortographic projection? Play with the arrows gizmo in the upper right corner of the scene view to set it to perspective, or to view scene from another side.

It is in orthographic projection. I click Main Camera in the Hierarchy, and try to change from that to Perspective, but it won’t let me change it.