@kodoly7 Thanks for the additional info. The experimental on-demand-loading package currently has a dependency to the spine-unity UPM package, which is not detected by the Unity Package Manager when installed as unitypackage. So the solution would be to either uninstall the spine-unity package from the unitypackage and re-install it via the Unity Package Manager (spine-csharp and spine-unity), as described here.
An alternative would be to remove the dependency line
"com.esotericsoftware.spine.spine-unity": "4.2.21"
from the package.json inside the com.esotericsoftware.spine.on-demand-loading package directory. To be able to modify the package.json file, you might need to clone the spine-runtimes git repository to a local directory, and then modify the file.
We're sorry for the inconvenience!
