The idea is to have something like a notification, a small GUI on screen that doesn't block the player but can also be clicked if the mouse cursor is visible. I know how to make overlay GUIs, i just can't figure out how to make the button clickable. Is it possible to do this? And if so how can i do this? 

I think he means when the notification appears, you can open your inventory for example to make the cursor visible and then click on the notification.

Kinda, instead of the inventory the player will open the chat, so the cursor become visibile and he can click on the notification.

Oh I'm just thinking, maybe while the notification is visible, you could use a MouseListener and know if the notification has been clicked or not.

I'm worry this could be heavy to handle. Consider that the mod will run on a server with many players, so handling mouse movement for every player could lead to some lag i guess

Right, i'm a bit confused on this. The mod runs on the server but the event happens on client, right. By the way i'll try that event

I tried that event, but i get some issues: the event is fired when the mouse is moved, not only when it's clicked, and if there are two GUI's opened, like the chat gui and the notification, it will take the chat gui because it's a GuiScreen. I also didn't get a way to check where the click happened  I guess i'll move on and discard this idea