I've had a conanfile.py which works fine if "conan install" is called from CMD, dependencies are built beforehand, and then CMake can find the targets.

But it does not if conanfile.py is given to QtC and leave everything to "package manager auto setup" as documentation describes:
https://doc.qt.io/qtcreator/creator-project-conan.html

I've attached the log. One can see that during configuration step, QtC tells Conan to run

conan install C:/dev/ConanTest/build/Desktop_Qt_6_9_2_MSVC2022_64bit-Debug/conan-dependencies -of=C:/dev/ConanTest/build/Desktop_Qt_6_9_2_MSVC2022_64bit-Debug/conan-dependencies/build/conan -pr;C:/dev/ConanTest/build/Desktop_Qt_6_9_2_MSVC2022_64bit-Debug/conan-dependencies/conan_host_profile;--build=missing;-s;build_type=Debug

I can only assume that is some "default" command that QtC issues. I certainly have no room to step in. And at the end, Conan fails to do what QtC asks:

[cmake] LINK : fatal error LNK1181: cannot open input file 'apps\app_rand.obj'

Beside, what did work is that, as aforementioned, call Conan commands from CMD, build everything manually beforehand, and let CMake use them. The Cona command that worked is:

conan install . --output-folder=build --build=missing -s build_type=Debug

BTW, a noticeable warning at the beginning of log is:

Qt Creator: conan package manager auto-setup. Skip this step by setting QT_CREATOR_SKIP_CONAN_SETUP to ON.

Maybe the problem is that "conan package manager auto-setup" does not work at all in the first place.