A user is trying to use compiler provided by Intel oneAPI (setting that as the compiler of a kit):

and consequently, the Clangd packed with Qt Creator does not seem to correctly recognize some APIs that it should, e.g. printf:

Notice that although Intel oneAPI is in use, the actual code is nothing special. It's just a minimal "Hello World" thingy. And "printf" should not be something so special and unrecognizable.

Although we allow Clangd binary from custom source, the one packed with Intel oneAPI:

$ /opt/intel/oneapi/2025.2/bin/compiler/clangd --version
Intel(R) oneAPI DPC++/C++ Compiler 2025.2.1 (2025.2.0.20250806)
Features: linux
Platform: x86_64-unknown-linux-gnu

is not recognized correctly by QtC. QtC complains about "Failed to retrieve clangd version: Unexpected clangd output".

By the way, this may or may not be related to QTCREATORBUG-28037 as it is suggested there that QtC not only accepts binary, but a script should also be fine. So it may be able to "trick" QtC that Clangd from Intel oneAPI (or whatever Clangd) produces reasonable output. If that is true, we may want to document that or implement some sort of configuration about that.