To get sound from an aftermarket source (e.g. YouTube, Spotify, Carplay), check if the head unit automatically switches to AUX. You need to watch this video and start at 3:27
Depending on where the AUX is positioned, you'll need to change Settings>Install Set>666888>Original Car AUX audio switch (change the number) >Save and reboot
On the picture below, it shows AM as number 1 then FM as number 2, and so on. And the AUX is on the 9th.