Why does the solidworks assembly drawing become blurry and unclear? The icons have also changed

This is when the assembly is selected for lighten or large assembly mode. When you open an assembly, some or all of the parts are automatically lightened to speed up the assembly. If you don't want to do this, you can remove the checkmark in front of Lighten or Large Assembly Mode below when you open the assembly, or you can select some or all of the parts in the open assembly, and right-click - Set to Restore.