Just tested it and the Bluetooth steps are unnecessary. Here are updated instructions. Much easier.
Open the shortcuts app
click on the blue plus sign in the top right corner.
then on the next screen click the three dots symbol in the same spot and name your shortcut whatever phrase you want
next click add action and choose the one marked scripting
In the Apps section and hit open app
the hit the shaded section marked "Choose" and scroll down to the app you want like spotify and select it
then hit done in the top right corner.
Now if you are in the car and you want Spotify just say Hey Siri followed by whatever you named that shortcut. After Spotify is open you should be able to push play on the Bluetooth audio screen of your car and whatever station you were listening to last should play. Then you can say Hey Siri play “This is Chris Cornell in Spotify” for example and it will switch stations.
I would think the same steps could be used to open Waze, but I don't use that one. Seems crazy to go to this extreme and I hope Apple fixes this in the next update.