In the Inspector, you'll find an option called Image Optimization. You can use it to apply a degree of rescaling and visual effects to image assets. Most of the time it will benefit the performance and image quality, but there are use cases where you may want to deactivate it.
Such a case may occur when working with very high-res displays. With such setups, we recommend checking image quality with and without image optimization enabled. Publish a simple project with an image asset to your Player(s) and decide for yourself which setting you prefer.