I also had the texting issue. I solved it by installing google messages. It seems to be the stock samsung texting that it has the issue with.
Glad that worked for you.... I tried Google Messages, Pulse, Textra, Samsung Messages, and Verizon messages. None of them fix the issue of Google saying "Sorry, but this internet connection isn't strong enough at the moment" when trying to send a text or reply to a text when connected to a car's head unit via Android Auto. It's a known issue that is specific to Android 10, not an app issue. Google has acknowledged it and "is working on a fix" since Feb 6th. Sooooo, we might see a fix by August if it's like any of the other "urgent" issues that Google has addressed in the past.
Clearing the caches on Google and AA and deleting your car(s) will get you one message or a few minutes of messages. But then it is back to not able to send.