A few thoughts. A stuffy nose often results from one of two things: the inside of your nose becoming dried out or a reaction to contaminants. Starting with the second, CPAP manufacturers generally recommend using distilled water, emptying the tank each morning, and regularly cleaning the water tank, hose, and mask, and replacing the air filter. That eliminates mineral dust in the air and avoids the growth of mildew or algae. Those things can irritate your nose, especially if you have allergies or sensitivity.
Even if you're accustomed to a desert climate, a CPAP tends to dry out the tissues in your nose more than normal breathing. So supplementing humidity will reduce the problem. The amount of humidity in the CPAP air that feels comfortable and protects your nose is something you will need to determine for yourself. Your nose and lungs can be comfortable with much higher humidity than your skin. But there are a few considerations for how to get it there.
The CPAP machine is designed to use normal household air as the source. If you feed it extremely humid air, you risk mildew growing inside the machine. A room humidifier is fine, but avoid locating it right next to the CPAP machine. The room humidifier will raise the room humidity to a level comfortable for your body, but you will likely still benefit from additional humidity in the CPAP output.
People often find the most nose comfort and protection at very high humidity, but there are several things to be aware of. At high humidity, you need to keep the tank, hose, and mask clean to avoid mildew or algae growth, and you will probably need a heated hose to avoid condensation and water up your nose. The CPAP humidifier increases the humidity by raising the temperature of the tank water so it evaporates more easily (it doesn't actually get hot, just varying levels of warm). At high humidity levels, there is also a high dew point (the temperature at which the humidity condenses out of the air and becomes water again). This can happen at room temperature, resulting in water condensing in the hose and being blown into your nose. A heated hose keeps the air in the hose above the dew point.
So you may need to play with the hose temperature as well as the humidity level. Don't be afraid to set the CPAP humidity level high--that will give your nose the most protection. Check the hose in the morning for any signs of water droplets. If you see any (or if you experienced water up your nose), increase the hose temperature setting a little.
Because there are so many variables (you, your environment, etc.), people won't be able to recommend specific settings. It will require a little experimenting.
BTW, many people benefit from using a saline nasal spray. You can buy pre-made spray or make it yourself (good instructions at
https://www.wikihow.com/Make-Saline-Nasal-Spray).