In the given project, it is missing the PackedMode build script. Without that script, or another script that can build type 'AddressablesPlayerBuildResult' it does not know how to build. Since this is the case, the best thing we can do is try to direct the user to what they need to do by putting "No Build Script Available" in the dropdown for New Build and they can search that phrase in the documentation and it comes up with the full description of the problem.

To simply just build, they need to create a new Addressables project, get BuildScriptPackedMode.asset from that project as it is created by default, and add it to Assets/AddressableAssetsData/DataBuilders, then add it under AddressableAssetSettings Inspector "Build and Play Mode Scripts"

If they don't mind their settings getting deleted, they could also just delete Assets/AddressableAssetsData and click "Create Addressable Settings" in Addressables group window and it will re-generate everything addressables

Added this to the docs to explain in detail:

If under *New Build there is an unclickable No Build Script Available, check [`AddressableAssetSettings`](../api/UnityEditor.AddressableAssets.Settings.AddressableAssetSettings.html) in the Inspector and see **Build and Play Mode Scripts section. In order to show up under New Build in Addressables Groups window , there must be a build script [`ScriptableObject`](https://docs.unity3d.com/Manual/class-ScriptableObject.html) that is able to build type [`AddressablesPlayerBuildResult`](../api/UnityEditor.AddressableAssets.Build.AddressablesPlayerBuildResult) paired with an entry in the Build and Play Mode Scripts section of the Inspector window for `AddressableAssetSettings`.*
To add a new Build or Play Mode script, click the `+` under the *Build and Play Mode Scripts section and find your build mode asset. Once it is added, if the script is a Play Mode script it will show up under Window > Asset Management > Addressables > Groups > Play Mode Script. If the script is able to build [`AddressablesPlayerBuildResult`] it will show up under **Window > Asset Management > Addressables > Groups > Build > *New Build. Build and Play Mode scripts provided by default, including `BuildSciptPackedMode`, are located under `Assets/AddressableAssetsData/DataBuilders`. See earlier section "Build scripts" for more information on custom build scripts.