Can the chocolate mousse ganache cake be frozen?

I wouldn’t either. It’s unlikely that the mousse would retain its lift and texture after being frozen and thawed. You could make the cake ahead of time, let it cool completely, wrap it well and freeze it. Let it come to room temperature before working with it. And then make the mousse and ganache on the day you plan to serve it.

I've never tried to, but I probably wouldn't. I am always looking for desserts (and anything else!) that can be made ahead and frozen. Nigella Lawson has a chocolate mousse cake that is absolutely divine, which may be similar in most relevant respects to this one. Lawson (or her team) advise against freezing it. Here is their good explanation: https://www.nigella.com/ask/freezing-chocolate-mousse-cake

I'm interested though in hearing others' thoughts on this. ;o)