Deserts are hot asf, lack survival resources, require a lot of planning to traverse, and tend to be very anti-life in every aspect. If you're entering a desert, you'll be bringing a ton of necessities into it with the focus of it not spoiling during the journey. You'll also, if possible, will be route planning prior to entering so you can move to any watering points, landmarks, or sparse villages (if there are any) in order to resupply and rest. Move fast, move smart, beat the heat by moving at night, stave off freezing your ass off by dressing warm beneath the stars. Utilize the stars to navigate. Don't get lost. Good luck.
Savannahs tend to be easier to survive in due to the typical presence of animals (think Lion King, that's a savannah) and some forestry/plants that can be harvested. However, they are also anti-life in terms of Humans, Elves, etc. The animals here are very wild-focused and will include your characters in their food chain, and your characters will likely be at a disadvantage in a low fantasy setting (i.e; no magic and the like). But, with good wits and a strong team, you can traverse and sustain yourself in a savannah.
Edit: Just want to include that my MC was born in and lived in a desert setting. Had to do some research in it and plan things accordingly. Deserts are more habitable than you think and you can grow plenty of crops with proper farming knowledge. Like rice, for example. People have found ways to survive in the arid environment and you can do it in creative ways by just being smart about it.
