The wpilib setup for Windows does not support clang. It is known to break, but it shouldn’t be possible for it to show up either, especially as long as you have the roboRIO compiler installed.
In vs code on the right side of the status bar. There’s one that looks like a platform, right? Either windowsx86-64 or linuxathena. Click it, make sure one of the linuxathena options is selected, and then follow the instructions here to reset intellisense.