Install a dev environment - A bit lost

Hello everybody,

I'd like to, after some time to handle source code, do some bug correction.
But I think I'm lost beetween old and new ways to configurate a dev environment.

I installed Git and Cmake (on Windows).
I'd like to configure and IDE, so went through these pages and choose Qt Creator :
- https://musescore.org/en/handbook/developers-handbook/compilation/compi…
- https://musescore.org/en/handbook/developers-handbook/compilation/compi…

But everything seems outdated. I tried to go through anyway but some things are weird, like not working.
I've downloaded Qt 5.15 and MinGW 8.1 through the online installer.
I'm not really familiar with Qt and my last C++ dev was 10 years ago, I'm more a java guy. Maybe I misunderstood a lot a things. But I'm here, ready to learn and to be helpfull.

I can open the project with the CMakeLists but he /build.qtc doesnt exist, so I pointed my build config on /build folder (I saw it generates a .qtc folder inside it).
For the variable CMAKE_INSTALL_PREFIX, the win32install folder or file doesnt exist...
The project configuration doesnt work. Here is the log text.

[cmake] Exécute C:\Qt\Tools\CMake_64\bin\cmake.exe -S C:/Users/Zachary/MuseScore -B C:/Users/Zachary/MuseScore/build dans C:\Users\Zachary\MuseScore\build.
[cmake] CMake Deprecation Warning at CMakeLists.txt:23 (cmake_policy):
[cmake] The OLD behavior for policy CMP0091 will be removed from a future version
[cmake] of CMake.
[cmake]
[cmake] The cmake-policies(7) manual explains that the OLD behaviors of all
[cmake] policies are deprecated and that a policy should be set to OLD only under
[cmake] specific short-term circumstances. Projects should be ported to the NEW
[cmake] behavior and not rely on setting a policy to OLD.
[cmake]
[cmake]
[cmake] -- The C compiler identification is unknown
[cmake] -- The CXX compiler identification is unknown
[cmake] CMake Error at CMakeLists.txt:25 (project):
[cmake] The CMAKE_C_COMPILER:
[cmake]
[cmake] C:/Qt/Tools/mingw1120_64/bin/gcc.exe
[cmake]
[cmake] is not a full path to an existing compiler tool.
[cmake]
[cmake] Tell CMake where to find the compiler by setting either the environment
[cmake] variable "CC" or the CMake cache entry CMAKE_C_COMPILER to the full path to
[cmake] the compiler, or to the compiler name if it is in the PATH.
[cmake]
[cmake]
[cmake] CMake Error at CMakeLists.txt:25 (project):
[cmake] The CMAKE_CXX_COMPILER:
[cmake]
[cmake] C:/Qt/Tools/mingw1120_64/bin/g++.exe
[cmake]
[cmake] is not a full path to an existing compiler tool.
[cmake]
[cmake] Tell CMake where to find the compiler by setting either the environment
[cmake] variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
[cmake] to the compiler, or to the compiler name if it is in the PATH.
[cmake]
[cmake]
[cmake] -- Configuring incomplete, errors occurred!
[cmake]

Anyway, can I have some help to make a clean and working dev environment please ?
After that, I'll be more independant :-)