I found a mmenu native solution for this, use the "noSelector" configuration, like this:

const menu = new Mmenu("#menu", {
        // Options
        offCanvas: {
            position: "right-front",
        }
    },{
        // Configuration
        offCanvas: {
            page: {
                selector: "#page",
                noSelector: ["#footer"],
            },
        },
    });

Works for me. Regards