Safari on Mac (and iOS), In the Safari settings under Websites, Reader, you can set "Other Websites" to "On", and it's on by default except websites you turn of

Safari on Mac (and iOS), In the Safari settings under Websites, Reader, you can set "Other Websites" to "On", and it's on by default except websites you turn off (which you can do from the reader button on the left part of the address bar.)