Bluetooth does allow for sms, most cars now let you send basic texts however I found the problem.
Android Voice command software assumes it's installed on a phone, as such it sends the command to the "phone app", in the case of the android head unit, it doesn't use it, and often they use a custom "bluetooth" application. In older version of Android someone wrote an app that would intercept the command and redirect it to the custom app. I have not been able to find anything for android 10.