This post is for Helix Ultimate Version: 2.1.1, SPPB Version: 5.3.2, Joomla Version: 5.1.1, no Template is used.
Hello Toufiq, if i add a new Section, hit the "+" Button or "Add Elements" Button i can add the Addon i want to have in that Section.
https://i.imgur.com/LFh1akN.png
If the Layers window is opened no Addon can be added anymore. Even if i close the Layers window again, i cannot add any Addon until the page is reloaded again.
https://i.imgur.com/YTF3jtz.png
This behaviour started after you made the Layers window movable.
Video to reproduce is in Hidden Content.