I'm trying to understand why some icons are displayed correctly and some other not on a HiDPI display

Qt 5.15.2
KDE Plasma 5.23.90
2880 x 1800 display

Qt Code: 
  1. #include "mainwindow.hpp"
  2. #include <QApplication>
  3.  
  4. int main(int argc, char *argv[])
  5. {
  6.   QApplication a(argc, argv);
  7.   MainWindow w;
  8.   w.setWindowTitle("HiDPI test");
  9.   w.show();
  10.   return a.exec();
  11. }
To copy to clipboard, switch view to plain text mode 
Qt Code: 
  1. #ifndef MAINWINDOW_HPP
  2. #define MAINWINDOW_HPP
  3.  
  4. #include <QFileDialog>
  5. #include <QMainWindow>
  6. #include <QStandardPaths>
  7. #include <QStatusBar>
  8. #include <QToolBar>
  9. #include <QVBoxLayout>
  10.  
  11. class MainWindow : public QMainWindow
  12. {
  13.   Q_OBJECT
  14.  
  15. public:
  16.   MainWindow(QWidget *parent = nullptr);
  17.  
  18. private Q_SLOTS:
  19.   void settings();
  20.  
  21. private:
  22.   QToolBar *tool_bar_;
  23.   QAction *add_media_;
  24.   QAction *remove_media_;
  25.   QAction *get_info_;
  26.   QAction *download_medias_;
  27.   QAction *settings_action_;
  28.   QStatusBar *status_bar_;
  29. };
  30.  
  31. #endif
To copy to clipboard, switch view to plain text mode 
Qt Code: 
  1. #include "mainwindow.hpp"
  2.  
  3. MainWindow::MainWindow(QWidget *parent)
  4.   : QMainWindow(parent)
  5. {
  6.   QWidget *central_widget = new QWidget(this);
  7.   QVBoxLayout *layout = new QVBoxLayout;
  8.   central_widget->setLayout(layout);
  9.   setCentralWidget((central_widget));
  10.  
  11.   status_bar_ = new QStatusBar;
  12.   tool_bar_ = new QToolBar;
  13.   add_media_ = new QAction(QIcon::fromTheme("list-add"), "Add", this);
  14.   remove_media_ = new QAction(QIcon::fromTheme("list-remove"), "Remove", this);
  15.   get_info_ = new QAction(QIcon::fromTheme("documentinfo"), "Information", this);
  16.   download_medias_ = new QAction(QIcon::fromTheme("download"), "Download", this);
  17.   settings_action_ = new QAction(QIcon::fromTheme("settings-configure"), "Settings", this);
  18.   connect(settings_action_, &QAction::triggered, this, &MainWindow::settings);
  19.  
  20.   tool_bar_->addAction(add_media_);
  21.   tool_bar_->addAction(remove_media_);
  22.   tool_bar_->addSeparator();
  23.   tool_bar_->addAction(get_info_);
  24.   tool_bar_->addSeparator();
  25.   tool_bar_->addAction(download_medias_);
  26.   tool_bar_->addSeparator();
  27.   tool_bar_->addAction(settings_action_);
  28.  
  29.   layout->addWidget(tool_bar_);
  30.   layout->addWidget(status_bar_);
  31. }
  32.  
  33. void MainWindow::settings()
  34. {
  35.   QFileDialog *file_dialog(new QFileDialog);
  36.   file_dialog->setFileMode(QFileDialog::DirectoryOnly);
  37.   QStringList download_location(QStandardPaths::standardLocations(QStandardPaths::DownloadLocation));
  38.   file_dialog->exec();
  39. }
To copy to clipboard, switch view to plain text mode 
Qt Code: 
  1. cmake_minimum_required(VERSION 3.5)
  2. project(hidpi_test)
  3. add_compile_options(-Wall -Wextra)
  4. set(CMAKE_CXX_STANDARD 14)
  5. set(CMAKE_CXX_STANDARD_REQUIRED ON)
  6.  
  7. ## Find Qt5
  8. set(CMAKE_AUTOMOC ON)
  9. find_package(Qt5Widgets REQUIRED)
  10.  
  11. add_executable(
  12.   ${PROJECT_NAME}
  13.   mainwindow.hpp
  14.   mainwindow.cpp
  15.   main.cpp
  16. )
  17. target_link_libraries(
  18.   ${PROJECT_NAME}
  19.   Qt5::Widgets
  20. )
To copy to clipboard, switch view to plain text mode 

The + (list-add) and - (list-remove) icons are perfect but the others are pixelated. When opening a QFileDialog the buttons icons (New directory, Ok, Cancel) are pixelated too.

Screenshot_20220205_135455.jpgScreenshot_20220205_135322.png

How can I get all the icons right?