For defaulting to syntax on, if you have a configuration file (~/.vimrc), you need to manually specify that in your vimrc by adding "syntax on". Vim also comes with some better defaults (including turning syntax on) that you could just load in in your vimrc file (type ":h defaults.vim" to see how to do that)
Visual mode should work, how is it not working? You may want to be more descriptive when asking for help as it's a little hard to be able to help otherwise.
Vim can be installed via multiple ways. The default Vim installation (I imagine that is what you have?) is installed via macOS. You can't update that yourself as Apple manages that installation. Other popular methods include using Homebrew to manage Vim (go to
https://brew.sh for installation instructions), or if you want a GUI just download a MacVim binary from
https://macvim-dev.github.io/macvim/ which comes with an auto-updater to update MacVim for you.