I really hated when I found out I couldn't open Spotify with Siri. Here is what I did. Hope it helps.
I created a shortcut. This seems complicated but it really isn't. Here are the steps.
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
scroll down to the Devices section and choose Set Bluetooth the command should now appear with bluetooth on by default
click on the shaded section of the command that says "on" to set it to off
hit the plus button under the command to add another step
scroll back up to 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
hit the plus button to add the last command
scroll back down to the Devices section and choose Set Bluetooth again, this time leave it set to "on"
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. The iPhone will still need to be unlocked like it did before the update, wish I could fix that. After Spotify is open you should be able to push play on the Bluetooth audio screen and whatever station you were listening to should play. Then you can say Hey Siri play (and name another station and it will switch to that station.
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.