I have got task:

[Tasks]
Name: "backup"; Description: "Do backup"; Flags: unchecked

I need checkbox of this task to be unable to tick (“grayed out”/disabled) in case of fresh installation (not upgrading the application)

In my .iss file i have got function which checks if it’s an upgrade or fresh installation:

function CheckIsUpgrade: Boolean;

How to use that method to determine if “backup” task will be “grayed out”/disabled, or it will be enabled and user during installation will choose whether to do backup (tick checkbox) or not (leave checkbox unticked)