Visual Studio 2019 Issue With unity

Hi everyone, I'm new to to the Unity Forums so I apologize if this is in the wrong category or anything.

I recently upgraded from VS 2017 to 2019. When I did this I lost the ability to reference external namespaces with Unity. For instance, I cannot find the namespace using UnityEngine.AI and therefor can't use anything Nav Mesh related. I made sure that the Unity Extension for VS was installed, and that the .Net Framework was 4.0 or higher, and for the life of me can't figure out how to integrate 2019 with Unity. The only fix after many many hours, was to reinstall Unity and go back to VS 2017, which I hope does the trick but haven't been able to check yet

I was just wondering if anyone else has had any issues like this, or if there's something I missed? Not sure what happened