Hi I have had problems with VS all day now and do now wonder what’s wrong with my external tools section in preferences in unity. Now it looks weird and asks for some sort of diff/merge files:
“Open by file extension” => Can you change that to Visual Studio? Is that an option?
If not, check Package Manager. Perhaps un- and reinstall the Visual Studio package.
Here’s my full core dump:
This may help you with intellisense and possibly other Visual Studio integration problems:
Sometimes the fix is as simple as doing Assets → Open C# Project from Unity. Other times it requires more.
Other times it requires you also nuke the userprefs and .vsconfig and other crufty low-value high-hassle files that Visual Studio tends to slowly damage over time, then try the above trick.
Barring all that, move on to other ideas:
Also, try update the package inside of Unity: Window → Package Manager → Search for Visual Studio Editor → Press the Update button
Depending on flavor and version of Visual Studio, it may also have an installation step that you perform within the actual Visual Studio. This step seems finicky at best and may require multiple openings of VS before it comes up.
Update: The VSCode extension has been deprecated and abandoned:
Update: the VSCode integration is back… maybe!?
There may be a community fork available that is receiving updates.
Also, this: No suggestions in Vscode - Unity Engine - Unity Discussions
Recently (July 2023) I worked on a Windows11 system that required a Microsoft component to be installed from within Visual Studio before it would work properly with all the OTHER software installed under Unity. I have no documentation on that process as I have only seen it once and it surprised me as well.
Finally! It works again. Somehow the VS Editor package in unity got uninstalled. Reinstalling it and regenerating the .csproj files worked.
Could you provide guide how to add VS Editor package? I have identical problem 
Like mos packages its added via the package manager: Unity - Manual: Package Manager window
