Why doesn't TAB work in nvim?

Question

vim

Config from /.config/nvim/init.vim

set mouse=a  " enable mouse
set encoding=utf-8
set number
set noswapfile
set scrolloff=7

set tabstop=4
set softtabstop=4
set shiftwidth=4
set expandtab
set autoindent
set fileformat=unix

call plug#begin('~/.vim/plugged')

Plug 'morhetz/gruvbox'
Plug 'jiangmiao/auto-pairs'
Plug 'scrooloose/nerdtree'
Plug 'preservim/nerdcommenter'
Plug 'norcalli/nvim-colorizer.lua'
Plug 'vim-airline/vim-airline'
Plug 'vim-airline/vim-airline-themes'
Plug 'sirver/ultisnips'

call plug#end()                 

colorscheme gruvbox


let g:airline_theme='gruvbox'

" NERDTree
nmap <C-f> :NERDTreeToggle<CR>