It seems that the specified files could not be found. Could you please confirm whether the /home/fj/.oh-my-zsh/themes/ folder exists?
In my case, the themes are located at /usr/share/oh-my-zsh/themes/. Please refer to the screenshot below.
This is how my .zshrc looks like
# Lines configured by zsh-newuser-install
HISTFILE=~/.histfile
HISTSIZE=1000
SAVEHIST=1000
# End of lines configured by zsh-newuser-install
export ZSH="/usr/share/oh-my-zsh"
# Set the Zsh theme
ZSH_THEME="agnoster"
# Enable Oh My Zsh plugins
#plugins=(zsh-autosuggestions zsh-syntax-highlighting)
# Initialize Oh My Zsh
source $ZSH/oh-my-zsh.sh
# The following lines were added by compinstall
zstyle :compinstall filename '/home/dirn/.zshrc'
autoload -Uz compinit
compinit
# End of lines added by compinstall
fastfetch
source /usr/share/zsh/plugins/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh
source /usr/share/zsh/plugins/zsh-autosuggestions/zsh-autosuggestions.zsh