background image in slide-out side bar

Right now you would have to apply it to the primary menu if using the options.

You can use CSS though - do you want to add a BG image to the entire area, or just the menu items?

the entire area please.

Try this:

#generate-slideout-menu {
    background-image: url("URL HERE");
    background-position: center center;
}

Adding CSS: https://docs.generatepress.com/article/adding-css/

Let me know.

I will try that. Thank you.

You're welcome :) Let me know if it works out!