every time I try to type something on a clean sheet my letters ( no matter what font I use) look like someone cut through them. Can you help and tell me why is this happening?
Please update your operating system. The issue that you are seeing is a GPU rendering issue discussed here : https://illustrator.uservoice.com/forums/601447-illustrator-bugs/suggestions/20384572-high-sierra-macos-10-13-gpu-rendering-issues-wit
This was fixed in 10.13.4