Here’s a quick solution for people that are using unity 2019 and are trying to open C# scripts (or shaders) with visual studio.
The reason visual studio isn’t opening can be due to one of two reasons.
A) You got Microsoft SQL Server Management Studio open. For some odd reason, unity is sending the “open” command to SSMS instead of visual studio. Closing it fixes the issue.
B) you might need to update the package, to do so go to Window->Package Manager
It’s a really niche issue, but I hope this’ll help people that are pulling out their hairs 