I did end up getting Android Auto to work luckily. However, other things just went sort of south from there. My use case for GrapheneOS wasn't quite fit.
The built in firewall did work well enough for my usecase. However, I didn't want a DNS based adblocking solution as that took away from my ability to connect to my home VPN. I should reach out to see if they can help. However, I did end up switching back to LineageOS since I could use a custom kernel which significantly lowered the running temps of my phone.
I wanted to try DivestOS, but there isn't a Pixel 8 Pro build yet.
Huge fan of what GrapheneOS and the team/community have done to make it better. I am sure going to keep my eye on it going forward.