High ISO graininess is serious, what should I do?

It should be normal. First of all, we need to understand the main function of ISO, that is, normal exposure in dark environment or fixed aperture. The higher the ISO, the stronger the sensitivity, and the stronger the ability to capture light in dark environment, but its image quality will be sacrificed, which means more noise. So in general, ISO will not be set to such a high level. Use auxiliary light as much as possible or change the lens with large aperture. It is very useful to use high sensitivity unless you want to capture a moving object at night. Thanks for reading!