Got wrong default-font after qApp->setFont () on macOS

Hi there,
I have installed the font "JetBrains Mono" on windows10, centos8 and macOS 11.2.3. The application UI got correct font on both windows10 and centos8 after I change the default font of application. But the application UI got wrong font on macOS. the code as following

QString cJetBrainsMono ("JetBrains Mono");
QFont defaultFont (cJetBrainsMono, 8);
qApp->setFont (defaultFont);
if (qApp->font ().family ().compare (cJetBrainsMono) != 0)
qApp->setFont (QFontDatabase::systemFont (QFontDatabase::FixedFont));

PS: in debug mode, qApp->font ().family ().compare (cJetBrainsMono) is true on macOS, UI with wrong font