Backup script (copy it to root directory of your project and run it every time you want to make a backup)

backup

#!/bin/sh
set -e

cd -P -- "$(dirname -- "$0")" # chdir to script directory

out_file="$HOME/backup/$(echo ${PWD#$HOME/} | sed 's@/@,@g').tar.zst"

((git ls-files -z --cached --recurse-submodules 2> /dev/null &&
  git ls-files -z --others --exclude-standard &&
  PROJECT_DIR=$PWD git submodule foreach --quiet 'git ls-files -z -o --exclude-standard | while read -d "" x; do echo -n "${PWD#$PROJECT_DIR/}/$x"; echo -ne "\0"; done' &&
  echo -ne '.git\0'
  ) || ls --zero -A) | \
	xargs --null tar --create --zst --file "$out_file"

du -sh "$out_file"