It is very difficult avoiding digital noise, no matter the lighting. Sometimes it's more than others. To reduce the noise/grain on your photos a little post processing is required. Not much. Too much will take away the natural appearance, and/or introduce additional noise. One of the reasons for noise is your ISO setting. The higher the ISO the more noise introduced. It is recommended that you use the lowest ISO, however there are times (eg. late evening, or night) that you'll definitely require higher ISO settings. In this case you might require to adjust other settings that will allow the reduction of noise/grain. The best thing to do in this case is to get to know your camera. Read the manual and practice.
As I said before post processing is required in most cases, if not all. To inspect your photos for noise/grain, apply a 100 to 200% zoom. Look in the dark areas for digital noise, and in the smoother area for grains. Use the relevant noise reduction tool to reduce the chromatic and luminant noise. Since this process softens your photos, sharpening is also required. Read up as much as you can on photo editing and practice. Some of your photos will eventually be accepted. You can start with Create better photos for Adobe Stock with 7 tips for success | I hope this helps.
Best wishes.