"What are Input Switch Notifications?"

I enabled the settings and received a notification prompt asking if I wished to activate it, and it appears to be already activated. It seems like just the usual pop-up messages to me. But what does "Input" refer to? Input of what exactly? And what is meant by "Switch"?

I tried searching for "input switch Windows 11," but all the results relate to keyboard functionalities and nothing about what I am witnessing.