Not an editor command: PluginInstall after new Vundle installation on Windows 10

Question

I am trying to setup Vundle on Windows 10 (Version 20H2 OS Build 19042.630) and, after following these steps exactly (install git and curl from chocolatey, install gVim from here, clone Vundle) I am unable to use PluginInstall and instead get the following error: Not an editor command: PluginInstall. I can run vim and can confirm that a _vimrc exists at C:\Users\myusername\_vimrc and the `_vimrc currently contains (straight from the docs):

filetype off
set shellslash
set rtp+=~/vimfiles/bundle/Vundle.vim
call vundle#begin('~/vimfiles/bundle')
" let Vundle manage Vundle, required
Plugin 'VundleVim/Vundle.vim'

" All of your Plugins must be added before the following line
call vundle#end()            " required
filetype plugin indent on    " required
" To ignore plugin indent changes, instead use:
"filetype plugin on
"
" Brief help
" :PluginList       - lists configured plugins
" :PluginInstall    - installs plugins; append `!` to update or just :PluginUpdate
" :PluginSearch foo - searches for foo; append `!` to refresh local cache
" :PluginClean      - confirms removal of unused plugins; append `!` to auto-approve removal
"
" see :h vundle for more details or wiki for FAQ
" Put your non-Plugin stuff after this line