Look at vscode-clangd. The code-completion seems more robust (as long as you have suitable compile-commands.json) and it supports clang-tidy.

c_cpp_properties.json is a configuration file specific to Microsoft's C/C++ VSCode plugin. It's not used by clangd or clang-tidy.

Clangd and clang-tidy use compile_commands.json for configuration. Please see https://clangd.llvm.org/installation#compile_commandsjson for some discussion of this file and how to generate it.

Clangd does not use a clang-tidy executable; it links the libraries containing the clang-tidy check implementations into the clangd binary itself.

This design choice is fundamental to clangd's ability to provide clang-tidy diagnostics to the user with a low latency, because it means clangd can run the clang-tidy checker on the same AST that clangd uses to provide other editing features, and also that when the user makes an edit to a file, clangd can leverage the optimizations it implements to re-use most of the previous AST to re-run clang-tidy checkers quickly on the updated AST. If clangd were to call out to an external clang-tidy executable after every edit (which would parse the file from scratch each time), the latency of diagnostics being sent to the user would regress by an order of magnitude or more in typical projects.

(Taken from vscode-cpptools discussions). You need to set

"C_Cpp.loggingLevel" : "Debug"

in settings.json and then the commandline will appear in the C/C++ output pane.

Try putting the following in your workspace settings.json file:

"C_Cpp.codeAnalysis.clangTidy.useBuildPath": true

The setting's description:

If true and compileCommands is set, the -p=<build-path> argument is passed to clang-tidy instead of build arguments being passed after --. This may not work if environment variables aren't set so that system includes can be found.

From the help message for clang-tidy's -p flag:

-p <build-path> is used to read a compile command database.

    For example, it can be a CMake build directory in which a file named
    compile_commands.json exists (use -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
    CMake option to get this output). When no build path is specified,
    a search for compile_commands.json will be attempted through all
    parent paths of the first input file . See:
    https://clang.llvm.org/docs/HowToSetupToolingForLLVM.html for an
    example of setting up Clang Tooling on a source tree.

Somewhat related GitHub issue ticket in the vscode-cpptools repo: C_Cpp.codeAnalysis.clangTidy.useBuildPath should not add "compile_commands.json" to the -p argument #9273

I'm not sure if that will just work for you. If it doesn't try specifying the -p flag and build path manually (the path to the directory containing the compile commands JSON file) using the "C_Cpp.codeAnalysis.clangTidy.args" VS Code setting.