See https://trick77.com/slow-oh-my-zsh-loading-on-macos-11/

nvm lazy loading macOS zsh

# nvm lazy loading to prevent zsh loading delays on macOS (inspired by @insidewhy)
# Add this to the end of your ~/.zshrc but make sure to remove all existing nvm.sh related code from ~/.zshrc first.
NVM_SH=""
# nvm.sh location depends on installation method
if [ -s "/usr/local/opt/nvm/nvm.sh" ]; then # Homebrew installer location
  NVM_SH="/usr/local/opt/nvm/nvm.sh"
elif [ -s " ~/.nvm/nvm.sh" ]; then # Direct installer location
  NVM_SH="~/.nvm/nvm.sh"
fi
if [ ! -z "$NVM_SH" ]; then
  export NVM_DIR="~/.nvm"
  nvm_cmds=(nvm node npm)
  for cmd in $nvm_cmds ; do
    alias $cmd="unalias $nvm_cmds && unset nvm_cmds && . $NVM_SH && $cmd"
  done
fi