android compose UI focus issue

when I use IconButton  it can't get focus correctly , the  onFocusChanged function only invoke when I click it but it can't invoke when left/right key press , it seems can't find focus automaticly but only can find focus when click it , which is really confuse me a lot , but after i remove .fucosable(true)  property  , everything works fine , it can find focus correctly .   I still don't know the theory but it seems like a trap ,  we set focusable(true) to let this element can have focus ability but why this cause the unexpcetation behavior which really make me confusion.  hope someone encounter same issue as me can find that .  btw I am making TV/STB application so the focus is very important so this really consume me a lot time to find out