Since off-roading is your primary goal, I would look into Specialized or other established mountain bike manufacturers.
I have not heard of a folding mountain bike. Brompton is the defacto leader when it comes to folding bicycles but they are expensive (you are paying for the quality of their name and their patented folding design).
I have a non-electric Brompton. You can go off roading with it, but I would not recommend it. It does not do well on sand either. You can change the tires that come with the bike, but you are talking about after-market parts on a bike that is super expensive already. Even more so with an electric version.
Another folding bike leader is Dahon but I know less about what they offer.