Systemd run script after GUI is ready?

I’m running raspbian on pi. I’ve created a systemd script which runs a node.js app on startup.

Script:

#!/usr/bin/env bash
cd /home/pi/pop_machine && /usr/bin/npm start

Systemd Service:

[Service]
ExecStart=/home/pi/pop_machine/start_pop.sh

[Install]
WantedBy=default.target

The script works if I run it manually but not on startup. I’m wondering if it’s because it tries to run before its dependencies.

I’ve seen people require networking before running by adding a line to [install] is there something similar where I can wait until everything to run a GUI application is ready?

I assume I just need x-window?