For example, Update messages from Avast can interfere with the fullscreen mode of programs. Therefore, you should activate the game mode on before you start such programs, to disable the message temporary.
Avast Antivirus: game mode setting enable
When activated, game mode, Avast automatically detects whether a fullscreen application is open and taking messages and Pop then ups to disrupt the full-screen mode. To enable the mode:
Under Windows you should find in in the System Tray at the bottom right is a small icon of Avast, if you click on the arrow "show hidden icons". After right-clicking on the icon, you can simply press on the "silence/game mode".
If you can't find the icon, then open Avast and click in the left bar, click settings.
Under the point "General" you will find the settings for the game mode. Just scroll down a bit. There you can set the hook in front of the corresponding Option (see image).
The best settings for Avast we have them here collected.