After you apply this update for Microsoft Skype for Business 2016 or Skype for Business 2015 (Lync 2013), the following options are still available even though you apply the EnableFoldersInTabList client policy entry:
Tools > General > Reopen my conversation when i sign in
Tools > IM > Enable Tabbed Conversation
How to get this update
To get this update,
For Skype for Business 2016, install the January 2, 2019, update (KB4461586).
For Skype for Business 2015 (Lync 2013), install the January 2, 2019, update (KB4461557).
Note Lync 2013 was upgraded to Skype for Business in April 2015.