There seems to be an issue with LeanTween effecting how lists are rendered in the inspector in 2021 or higher. The problem is specific when LeanTween is added to a project with NaughtyAttributes project. This error is easy to reproduce by starting a new project in 2021, create a script with a list of objects, and add to a an object in the hierarchy. Populate the list or add some indexes with empty slots. Now add LeanTween and NaughtyAttributes packages and then examine the list. You will see that the slots no longer render. The work around is to use the NaughtyAttributes Reorderable List tag and the list will render. I have contacted Unity support and they advised contacting you and NaughtyAttributes about the issue.
There seems to be an issue with LeanTween effecting how lists are rendered in the inspector in 2021 or higher. The problem is specific when LeanTween is added to a project with NaughtyAttributes project. This error is easy to reproduce by starting a new project in 2021, create a script with a list of objects, and add to a an object in the hierarchy. Populate the list or add some indexes with empty slots. Now add LeanTween and NaughtyAttributes packages and then examine the list. You will see that the slots no longer render. The work around is to use the NaughtyAttributes Reorderable List tag and the list will render. I have contacted Unity support and they advised contacting you and NaughtyAttributes about the issue.