mountain biking will lead to weight loss. but it has more to do with your diet.
i think you really need to vary the workout a little. run one day, bike the next, walk the next, swim the next… etc. your body will get used to the same thing, even if you slowly keep going longer and gaining endurance.
you don’t necessarily NEED to lift - BUT - if you lift for 45 mins or an hour, then do some cardio right after, you will lose more weight faster. lifting burns up all of your body’s excess stored energy quickly, then then cardio will start burning down the fat cells faster.