I have a few classes which’s structure looks like this–

class App
{
     // Basic structure of the app
}

class Win32Window
{
    // Window functionality
}

class Win32Input
{
   // Input functionality
}

class Graphics
{
   // Graphics functionality
}

All of those are singleton classes as i plan to have no more than one instance of those in my program.
Now suppose if another class inherits those like this —

class SomeClass final: public App, public Win32Window, public Graphics, public Win32Input
{
   // Overrides some virtual methods of base classes or use their implementation
}

Now, is this kind of inheritance bad? To my knowledge it won’t have the Diamond problem that multiple inheritance typically has.

I am not having any problem using this way of inheritance but i want to know if it’s bad practice