Since Leetcode uses the standard library implementation of g++ 14, you need to disable default Clang's include paths and add the include paths of g++- 14 instead.
To achieve this easily, you can use just clangdw, a Clangd wrapper that automatically generates compile_flags.txt file for you.
Note g++-14 must be installed on your system to use this tool.
If you want to customize compile_flags.txt, you can just edit this file manually once it is generated.