Right-click in code editor window and choose Soldity Code Generation -> Solidty: Compile and Code Generate CSharp contract definition
Compilation starts but no csharp code files are generated. (abi, bin and json files are generated though.)
Workaround is to click twice (once immediately and then again after the message "Compiler using remote version: 'latest', solidity version: 0.8.28+commit.7893614a.Emscripten.clang" appears) in the code editor window, as the problem seems to be that the Output window gets focus immediately preventing the plug-in from finding the correct window. (Noticed that the plug-in code uses vscode.window.activeTextEditor - maybe this is the wrong window because of the focus change?)