When i click on the green (1.jpg)
Thunderbird show the activity board.
But it is empty. (2.jpg)
Is this okay?
I did not know you could even do that! 
The indicator closed too fast for me to click, but clicking anywhere on the Status Bar opened the Activity Manager in 81.0b3 for me using an en-US version.
Again, I did not even know you could do that!
If you have any extensions installed, try safe mode using Help > Restart with Add-0ns Disabled.
I do that, when i see a long time the green bar, to see what happens.