Vim entering normal mode when option + 8 or 9 - vim

Question

While in insert mode, my vim is entering normal mode when I press the key: option + 8 or 9, this corresponds to a [ or ], respectively on my mac. To write code this is really annoying, as I need brackets a lot. How can I remove this? Thank you.
I attach below my .vimrc file.
I have changed the esc key in inoremap to "jk" and the map leader key to ";".
Update: My terminal is alacritty, and there I don't have this problem. Only in vim.
" Disable compatibility with vi which can cause unexpected issues.
set nocompatible
" Enable type file detection. Vim will be able to try to detect the type of file in use.
filetype on
" Enable plugins and load plugin for the detected file type.
filetype plugin on
" Load an indent file for the detected file type.
filetype indent on
" While searching though a file incrementally highlight matching characters as you type.
set incsearch
" Enable auto completion menu after pressing TAB.
set wildmenu
" Make wildmenu behave like similar to Bash completion.
set wildmode=list:longest
" There are certain files that we would never want to edit with Vim.
" Wildmenu will ignore files with these extensions.
set wildignore=*.docx,*.jpg,*.png,*.gif,*.pdf,*.pyc,*.exe,*.flv,*.img,*.xlsx
:set relativenumber
:set number
:set autoindent
:set tabstop=4
:set shiftwidth=4
:set smarttab
:set softtabstop=4
:set mouse=a
:colorscheme iceberg
set termguicolors
set t_Co=256
set background=dark
set term=xterm-256color
set foldmethod=indent
set foldnestmax=10
set nofoldenable
set foldlevel=2
syntax on
syntax enable
" Highlight cursor line underneath the cursor horizontally.
set cursorline
set backspace=indent,eol,start
" Highlight cursor line underneath the cursor vertically.
set cursorcolumn
set list
set showbreak=↪\
set listchars=tab:→\ ,eol:↲,nbsp:␣,trail:•,extends:⟩,precedes:⟨
call plug#begin('~/.config/nvim/plugged')
Plug 'https://github.com/tpope/vim-commentary' " For Commenting gcc & gc
Plug 'https://github.com/tc50cal/vim-terminal' " Vim Terminal
Plug 'https://github.com/ryanoasis/vim-devicons' " Developer Icons
Plug 'https://github.com/neoclide/coc.nvim' " Auto Completion
Plug 'https://github.com/preservim/nerdtree' " NerdTree
"Plug 'ap/vim-css-color'
Plug 'ryanoasis/vim-devicons'
Plug 'vim-airline/vim-airline'
Plug 'Xuyuanp/nerdtree-git-plugin'
Plug 'tiagofumo/vim-nerdtree-syntax-highlight'
Plug 'airblade/vim-gitgutter'
Plug 'ctrlpvim/ctrlp.vim' " fuzzy find files
Plug 'scrooloose/nerdcommenter'
Plug 'christoomey/vim-tmux-navigator'
Plug 'morhetz/gruvbox'
Plug 'HerringtonDarkholme/yats.vim' " TS Syntax
Plug 'https://github.com/terryma/vim-multiple-cursors' " CTRL + N for multiple cursors
Plug 'vimwiki/vimwiki'
set encoding=UTF-8
call plug#end()
let g:vimwiki_list = [{'path': '~/vimwiki/',
\ 'syntax': 'markdown', 'ext': '.md'}]
nnoremap <C-n> :NERDTree<CR>
inoremap jk <ESC>
" Set the backslash as the leader key."
let mapleader = ','
nmap <C-n> :NERDTreeToggle<CR>
vmap ++ <plug>NERDCommenterToggle
let g:NERDTreeGitStatusWithFlags = 1
tnoremap jk <C-\><c-n>
nmap <F8> :TagbarToggle<CR>
let &t_SI.="\e[5 q" "SI = INSERT mode
let &t_SR.="\e[4 q" "SR = REPLACE mode
" Have nerdtree ignore certain files and directories.
let NERDTreeIgnore=['\.git$', '\.jpg$', '\.mp4$', '\.ogg$', '\.iso$', '\.pdf$', '\.pyc$', '\.odt$', '\.png$', '\.gif$', '\.db$']

Answer 1

The problem was in my alacritty terminal. Fixed it by changing the alacritty.yml config to:
alt_send_esc: false