I essentially copy-pasted SlippinJimmy’s post with some edits because I have the same issues, have tried the same things, but have not found a solution.
I’ve tried ‘turning it off and on again’. I’ve definitely got the visual studio code package installed as you suggest in the intellisense help page. Whenever I try to set Visual Studio Code as the external script editor in Unity: Edit > Preferences > External Tools, it seems to revert back if I close and reopen my project and navigate to that same window again, however vs code is indeed still being used as the default editor when I open the scripts in Unity.
I’ve installed .NET 6.0 and .NET Core isn’t available for download on that page. I have also downloaded .NET Framework 4.7.1 (Developer Pack) as suggested by Nina. This hasn’t fixed the issue. “Omnisharp: Select Project” in VS code also doesn’t fix the issue.
One thing I was unable to do was tweak the settings of the C# extension so that “Omnisharp: Use Global Mono” is set to “always” as this isn’t an option when I scroll through the Extension Settings list. I am using the same C# installation from Microsoft as is shown in the screenshots for Intellisense. And that’s the end of the intellisense help page so that’s why I’m posting this here.
This is beyond frustrating at this point. I’m ready to give up on it being fixed. I feel like I’ve just bloated my computer installing 100 different things that are having no effect.