I see said the blind man. Well I would assume that you are correct that if the BT symbol shows up you are connecting automatically. I think you can use Bixby to start AA for you as a routine. I haven't looked at it in a while but I believe BT is one of the triggers and Bixby can open apps. I'll try to look at it this evening and post something tomorrow but in the meantime, you could look through routines and see what you can figure out. You might Google it too, if it can be done someone has posted about it because someone else has had this question, or at least it seems common enough to be possible.
It's an extra step now to save a step later.
My Toyota is older and only works with that app and doesn't do AA at all. yah me. I gave up on it so long ago that I can't even remember, but I think I can do some version of AA on my phone and play sounds through a wired connection. The stereo won't do Google Maps at all, navigation is only possible with a special app exclusive to Toyota that should only have half a star on the Play Store, if that, and it costs. Imagine that, but I digress. Look at Bixby, she can do it I'm pretty sure. Yes Bixby is a her, always sounded like a masculine name to me, like a butler not a maid, but Samsung sees it differently I guess.
Let us know what you find.