Basically it affects the behavior of Buttons in Solo Frames.
For some reasons, over the years we ended up having cases where it was possible to have more than one button active at the same time in a Solo Frame.
While this allowed specific usage cases to be covered, it was clashing with the original idea written in the documentation:
Attached a simple workspace showing what was possible (Chaser and Scenes in a Solo Frame). With 4.11.0 it doesn't work anymore.A Solo Frame is almost exactly the same kind of a container as a normal Frame in that can hold various widgets and other frames inside. However, the difference with Solo Frame is that it treats any Buttons inside it differently by allowing only one button to be enabled at a time.
So I decided to allow you to vote what you want. My opinion is not relevant here, as what counts the most for me is to have happy QLC+ users.