GooDee YG420 mini projector doesn’t support Wi-Fi, but you can connect the projector to your iPhone via a wired way.
You can use a Lightning to HDMI Adapter, and then use the HDMI interface to connect to the projector. Here are the details.
Credit: Esbeecables
Get a Lightning to HDMI converter cable
Connect iPhone to your projector with the two ends of the Lightning to HDMI converter. Plug one end to the HDMI interface of GooDee YG420 and the other side to your iPhone.