Running is a great cardio exercise, it's free and you don't need any special equipment to do it. This video will help you improve your running technique.
Remember that if you do choose to go running, it's important follow current advice about staying a safe distance away from other people and not going out more than once a day.
Reverse lunges isolates the muscles in the glutes, lower limbs and stabilises the core. By varying intensity you'll improve your strength and endurance as well as stabilise the whole body.