When using neovim on macOS (at least macOS), text that is selected isn't automatically added to the primary selection for the operating system. One must use the terminal's selection utilities, or yank the text to the clipboard. I am unable to find a setting that will, upon selection update, add the selection to the primary selection. Is this possible?
Updated to add that this is not unique to neovim. I just tested, and the behavior is the same in vim.