1. Move everything to ~/.config/ghostty/.
2. Install zsh.
3. Install powerlevel10k in ~/.powerlevel10k.
4. Set command = .. to the .zsh binary, e.g. command = /usr/bin/zsh.
5. Add .zshrc these lines:

# <<< ghostty
if [[ "$TERM_PROGRAM" == ghostty ]]; then
	# enables powerlevel10k
	source ~/.config/ghostty/startup.zsh 
fi
# >>> ghostty

Great, you are set!