CMake does not set the compiler option -std to gnu17 or c++17 although I set the target_compile_features to cxx_std_17

Usage
12

I cannot reproduce that either:

$ cat ../CMakeLists.txt
cmake_minimum_required(VERSION 3.19)
project(Forum3299 CXX)
set(CMAKE_CXX_STANDARD 11)
add_library(example STATIC example.cxx)
target_compile_features(example PRIVATE cxx_std_17)

$ cmake ..
-- The CXX compiler identification is GNU 11.0.1
...

$  grep CMAKE_CXX_STANDARD_COMPUTED_DEFAULT CMakeFiles/*/CMakeCXXCompiler.cmake
set(CMAKE_CXX_STANDARD_COMPUTED_DEFAULT "17")

$ make VERBOSE=1 
...
/usr/bin/c++   -std=gnu++17 -o CMakeFiles/example.dir/example.cxx.o -c /.../example.cxx
...