The edges of my eraser brush are sharp at 100% hardness, but as the edge gets softer the edge of my brush gets diffused/pixilated. It makes it very hard to follow the edge of an image since the brush edge isn't sharp and it doesn't start to erase till the middle of the diameter of the circle. I attach a sample of the brush edge at 0% hardness, showing where it starts to erase. I tried resetting the tool and have futzed with the brush settings. Nothing seems to work. This just started happening.
On your Mac click your desktop then go to Apple>System Settings>Accessibility>Display and set
the Pointer Size to Normal
What version of photoshop and macOS are you using?
Does this happen when the Eraser Tool is 100% hardness or when you adjust the hardness lower than 100%?
In photoshop you can go to Photoshop>Settings>Cursors and set the Painting Cursors to Normal and see if that's any better.