You can run cmake with extra -D parameters to specify the location of taglib.
Configure using TAGLIB_INCLUDE_DIRS, TAGLIB_LIBRARY_DIRS and TAGLIB_LIBRARIES.
To find the include directory, look for the directory containing tag.h and use the parent directory of the "taglib" directory.
To find the library directory, look for libtag.dylib.
Something like this:
cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_PREFIX_PATH="/opt/homebrew/opt/qt6/lib/cmake" -DBUILD_WITH_QT6=ON -DUSE_BUNDLE=ON -DICU_ROOT="/usr/local/opt/icu4c" -DTAGLIB_INCLUDE_DIRS="/opt/homebrew/opt/taglib/include" -DTAGLIB_LIBRARY_DIRS="/opt/homebrew/opt/taglib/lib" -DTAGLIB_LIBRARIES="/opt/homebrew/opt/taglib/lib/libtag.dylib"I didn't test this, modify the dirs if they are wrong.