CarPlay and switching music sources

Hello! I’ve seen this problem try and be handled but none are exactly answering my question. I was a user of the Apple Music app for a really long time, but recently I switched to using Spotify and tend to prefer it now more than anything. My issue is that whenever the Bluetooth connects in my car, it’s a gamble in whether or not it will open Spotify or play some random playlist I don’t even have saved in my Apple Music. Sometimes I won’t listen to Apple Music for many months and it will still start play when I turn on my cars Bluetooth, even if the app wasn’t opened before. So I’ve been instructed by tutorials to turn off my CarPlay feature. Will this make it so that no music apps will connect to my cars bluetooth or just Apple Music? And if it makes it so that no music plays in the car if i turn it off, what can I do to make my main source Spotify instead of Apple Music without turning off CarPlay? Thank you!