zshrc outputing cryptic errors on iterm2 at loading - bash

Question

I am a Mac user on osx 10.15.7 (Catalina).
I recently updated brew and upgraded formulas with it.
Since then, my terminal has become erratic and prints out these errors:
_zulu_init_setup_completion:9: compinit: function definition file not found
/user/path/.zulu/packages/tipz/tipz.zsh:86: add-zsh-hook: function definition file not found
_zulu_init:48: promptinit: function definition file not found
_zulu_init:50: command not found: prompt
/user/path/.zprezto/init.zsh:14: is-at-least: function definition file not found
prezto: old shell detected, minimum required: 4.3.17
/user/path/.zshrc:19: promptinit: function definition file not found
/usr/local/Cellar/zplug/2.4.2/autoload/init.zsh:16: colors: function definition file not found
polling.zsh:17: add-zsh-hook: function definition file not found
# the following line is repeated at least 20 times
__zplug::core::core::get_interfaces:49: regexp-replace: function definition file not found
__zplug::core::core::prepare:67: compinit: function definition file not found
[zplug] ERROR: The loading of zplug was discontinued.
/user/path/.nvm/bash_completion:87: bashcompinit: function definition file not found
/user/path/.nvm/bash_completion:88: compinit: function definition file not found
/user/path/.nvm/bash_completion:95: command not found: complete
/user/path/.zshrc:35: command not found: gcloud
/user/path/google-cloud-sdk/completion.zsh.inc:1: bashcompinit: function definition file not found
/user/path/google-cloud-sdk/completion.zsh.inc:4: compinit: function definition file not found
/user/path/google-cloud-sdk/completion.zsh.inc:37: command not found: complete
/user/path/google-cloud-sdk/completion.zsh.inc:62: command not found: complete
/user/path/google-cloud-sdk/completion.zsh.inc:63: command not found: complete
I am not very versed into bash I think my installation might have been way to complex also (oh-my-zsh, prezto, powerlevel10k).
I just would like to know how to weed out the error and fix this.
my zshrc looks as follow
#
# Executes commands at the start of an interactive session.
#
# Authors:
# Sorin Ionescu <sorin.ionescu#gmail.com>
#
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"
# Initialise zulu plugin manager
source "${ZULU_DIR:-"${ZDOTDIR:-$HOME}/.zulu"}/core/zulu"
zulu init
# Source Prezto.
if [[ -s "${ZDOTDIR:-$HOME}/.zprezto/init.zsh" ]]; then
source "${ZDOTDIR:-$HOME}/.zprezto/init.zsh"
fi
# Customize to your needs...
autoload -Uz promptinit
promptinit
# Add RVM to PATH for scripting. Make sure this is the last PATH variable change.
# Add RVM to PATH for scripting. Make sure this is the last PATH variable change.
# Add RVM to PATH for scripting. Make sure this is the last PATH variable change.
# export PATH="$PATH:$HOME/.rvm/rubies/ruby-2.4.1/bin/"
# loading ZPLUG
export ZPLUG_HOME=/usr/local/opt/zplug
source $ZPLUG_HOME/init.zsh
export NVM_DIR="$HOME/.nvm"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm
[ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion" # This loads nvm bash_completion
export PATH="$HOME/.yarn/bin:$HOME/.config/yarn/global/node_modules/.bin:/user/path/Library/Python/3.7/bin:$PATH"
export GOOGLE_PROJECT="$(gcloud config get-value project)"
export GOOGLE_APPLICATION_CREDENTIALS="/user/path/PROJECTS/personal/k8s/gcp-k8s-credentials.json"
# The next line updates PATH for the Google Cloud SDK.
if [ -f '/user/path/google-cloud-sdk/path.zsh.inc' ]; then . '/user/path/google-cloud-sdk/path.zsh.inc'; fi
# The next line enables shell command completion for gcloud.
if [ -f '/user/path/google-cloud-sdk/completion.zsh.inc' ]; then . '/user/path/google-cloud-sdk/completion.zsh.inc'; fi
# iziwork key
export GITHUB_AUTH_TOKEN=xxx
EDIT
Bash Version : echo $BASH_VERSION gives a blank line.
Zsh Version : 5.7.1

Answer 1

prezto: old shell detected, minimum required: 4.3.17
Check your zsh version
zsh --version

Answer 2

In the end there were several issues, following the upgrade of brew some path did not get properly upgraded in the .zshrc file:
fpath in ~/.config/zulu was pointing to an older or incorrect version of zsh (particularly .../zsh/function)
path for zplug was incorrect
some gcloud command called before setting the path to gcloud
so
#this
/usr/local/Cellar/zsh/5.8/share/zsh/functions
#became
/usr/local/Cellar/zsh/5.8_1/share/zsh/functions
and
#this
export ZPLUG_HOME=/usr/local/Cellar/zplug/2.4.2/autoload/zplug
#became this
export ZPLUG_HOME=/usr/local/Cellar/zplug/2.4.2