A: You need to ensure that your solution is open in VS Code (not just a single file). Open the folder with your solution and you usually will not need to do anything else. If for some reason VS Code has not selected the right solution context, you can change the selected project by clicking on the OmniSharp flame icon on the status bar.
OmniSharp Flame on the Status Bar
Choose the -CSharp version of the solution file and VS Code will light up.
=> I don't have an OmniSharp flame icon
=> I don't have a -CSharp.sln solution file
Please advise, I desperatedly want the missing functionality
Issue 135 has been closed prematurely: vscode no longer autocompletes c# nor Unity API's
As suggested, I removed the Omnisharp extension, and the problems remain :(
Quoting from 'Unity Development with VS Code':
=> I don't have an OmniSharp flame icon => I don't have a -CSharp.sln solution file
Please advise, I desperatedly want the missing functionality