whenever I use the usb-c to aux adapter, everything works fine, except the phone App opens over whatever app I am using, whether its Spotify, Google podcast or google Maps. I tried disabling android auto to see if that helped, but it didn't. And its not only on my phone, it also happens on my wife's pixel 3 xl and my daughter's pixel 3A xl.
I have the same problem. It does this both on my S20 Ultra and Huawei P30 Lite. Couldn't find any solution on the internet. I'm sure it's the adapter but I can only buy a better one.