The problem you're having is with your step 3. You need to open the vimball file in NeoVim and the command to do so is
:e and not
:vim is actually a shorthand for
:vimgrep, that's why your error message is talking about "invalid pattern", it's expecting at least two arguments, one pattern and one base path where to run a recursive grep.
After loading the vimball package with
:packadd vimball and opening the netrw vimball with
:e netrw.vba, all you need is to run it with
:so % to install it.
By default, the vimball plug-in will unpack the plug-in files directly under your
~/.config/nvim. That's the older scheme pre-Pathogen where you would merge all the plug-in files into a single directory, rather than update
'runtimepath' to include the root directory of each of your plug-ins.
If you want to unpack the vimball into an alternate location, you can also call
:UseVimball directly instead of calling
:so % after opening the
*.vba inside NeoVim/Vim.
For example, to turn the netrw vimball into a NeoVim package:
:!mkdir -p ~/.local/share/nvim/site/pack/netrw/start/netrw
(For Vim, you can do the same, just use
~/.vim/pack on Linux/Mac/Unix or
$HOME/vimfiles/pack on Windows as the base package directory.)