It happens with latest version of official asset store tools:
https://forum.unity.com/threads/issue-asset-store-tools-not-working-in-2020-2.1023478
NullReferenceException: Object reference not set to an instance of an object
AssetStoreClient.get_ActiveSessionID () (at :0)
AssetStoreClient.get_HasActiveSessionID () (at :0)
LoginWindow.get_IsLoggedIn () (at :0)
AssetStoreManager.ValidateAssetStoreLogout () (at :0)
Existing lastest release for Unity 2020.1 doesn't work on 2020.2 either. Further investigation on this issue needed.