Hi Petri, thank you for your questions.
We are continuing to make investments in Skype for Business and the Technical Adoption Program provides a way for early adopters to help us validate that we are on track. Many of our valued SfB customers have followed our recommendation and moved to Teams, but there is a subset remaining on Skype for Business, and this TAP is geared towards them.
Microsoft will continue to support Microsoft Lync Server 2013, Skype for Business Server 2015, and Skype for Business Server 2019 through Microsoft’s Fixed Lifecycle Policy that covers customers through Mainstream and Extended Support phases.
For customers running Lync Server 2013, Skype for Business 2015 or Skype for Business 2019 and a down level CU, the recommendation is to upgrade to Skype for Business 2019 and the current CU/SU combination, so that any new functionality is available.