Currently, there is no official support for Unity 6 in the Spine runtimes. The latest supported versions are listed on the Spine Unity Download page. It is recommended to use the latest stable versions of both Unity and Spine to ensure compatibility. If you are experiencing issues with importing Spine animations, please ensure that you are using matching versions of the Spine Editor and the Spine-Unity runtime.

For now, it would be best to revert to a supported version of Unity until official support for Unity 6 is announced.

Mirkobil but my Spine animations are not working and are not even importing into the scene.

While it's not officially supported due to being in beta, in general there should be no such issues with Unity 6. Likely your setup is wrong.

Which exact version of the spine-unity runtime are you using (name of the unitypackage, also listed in Assets/Spine/version.txt or in the Unity Package Manager)?
Which version of the Spine Editor?

Saying your "Spine animations are not working" is too imprecise for us to help. Do you see any compile errors? Do you get error messages or dialogues?

You are saying "not even importing into the scene", but does it import in the project window and generate the assets like SkeletonDataAsset properly? Is the SkeletonDataAsset showing any error messages? Did you see error messages when importing your skeleton?

@Mirkobil Glad to hear, thanks for letting us know. It's strange that it didn't allow the drop on the Hierarchy panel initially. It might have been some incorrect state of the Unity project internals.