@Director The problem is located in the ProjectSettings/GraphicsSettings.asset
and is unrelated to Spine:
...
m_TransparencySortMode: 3
m_TransparencySortAxis: {x: 0, y: 1, z: 0}
..
This seems to be a leftover setting of your initial 2D project, sorting by Y axis instead of by depth.
If you change these two lines (using a text editor) to the following, it again sorts by the Z Axis (by depth) as desired:
m_TransparencySortMode: 0
m_TransparencySortAxis: {x: 0, y: 0, z: 1}
This can be considered a bug in Unity, as the Transparency Sort Mode
and Sort Axis
settings are not displayed in the Project Settings window when using a URP renderer, but they still seem to be used. Please report this bug over at Unity, so that they can fix this issue in future updates.