QtCreator not recognizing linked libraries after upgrading Ubuntu to 20.04

Same issue here, same solution as @nou. QtCreator 4.11 still relies on clang-8, but on Ubuntu 20.04 apt will install clang-10. The following solved the problem for me:

Install clang 8

sudo apt install clang-8

Update the alternatives

sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-8 100
sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-8 100

I had no need to re-install QtCreator.

I am not 100% sure that this is same problem but I solved it by installing clang-8 package. I think problem is that qtcreator code model plugin use libclang1-8 but clang-10 get installed by default.

It seems like Qt Creator 4.15.1 is again conflicting with it's default configured kits.

So I have made a custom one by:

• I have installed clang 10 from ubuntu.
• sudo apt install clang
• tools>options>Kits>Kits
• select the default Desktop QT 5.15.2 64 bit (default)
• Press Clone button
• In compiler section
• For C : Clang 10(C, x86 64bit in /usr/bin)
• For c++ Clang 10(C++, x86 64bit in /usr/bin)
• (Image attached)

Using this kit cmake and Qmake is working and also missing stl and std paths are fixed.