KDE Plasma HiDPI icons

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

Code:

#include "mainwindow.hpp"
#include <QApplication>
 
int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  MainWindow w;
  w.setWindowTitle("HiDPI test");
  w.show();
  return a.exec();
}

Code:

#ifndef MAINWINDOW_HPP
#define MAINWINDOW_HPP
 
#include <QFileDialog>
#include <QMainWindow>
#include <QStandardPaths>
#include <QStatusBar>
#include <QToolBar>
#include <QVBoxLayout>
 
class MainWindow : public QMainWindow
{
  Q_OBJECT
 
public:
  MainWindow(QWidget *parent = nullptr);
 
private Q_SLOTS:
  void settings();
 
private:
  QToolBar *tool_bar_;
  QAction *add_media_;
  QAction *remove_media_;
  QAction *get_info_;
  QAction *download_medias_;
  QAction *settings_action_;
  QStatusBar *status_bar_;
};
 
#endif

Code:

#include "mainwindow.hpp"
 
MainWindow::MainWindow(QWidget *parent)
  : QMainWindow(parent)
{
  QWidget *central_widget = new QWidget(this);
  QVBoxLayout *layout = new QVBoxLayout;
  central_widget->setLayout(layout);
  setCentralWidget((central_widget));
 
  status_bar_ = new QStatusBar;
  tool_bar_ = new QToolBar;
  add_media_ = new QAction(QIcon::fromTheme("list-add"), "Add", this);
  remove_media_ = new QAction(QIcon::fromTheme("list-remove"), "Remove", this);
  get_info_ = new QAction(QIcon::fromTheme("documentinfo"), "Information", this);
  download_medias_ = new QAction(QIcon::fromTheme("download"), "Download", this);
  settings_action_ = new QAction(QIcon::fromTheme("settings-configure"), "Settings", this);
  connect(settings_action_, &QAction::triggered, this, &MainWindow::settings);
 
  tool_bar_->addAction(add_media_);
  tool_bar_->addAction(remove_media_);
  tool_bar_->addSeparator();
  tool_bar_->addAction(get_info_);
  tool_bar_->addSeparator();
  tool_bar_->addAction(download_medias_);
  tool_bar_->addSeparator();
  tool_bar_->addAction(settings_action_);
 
  layout->addWidget(tool_bar_);
  layout->addWidget(status_bar_);
}
 
void MainWindow::settings()
{
  QFileDialog *file_dialog(new QFileDialog);
  file_dialog->setFileMode(QFileDialog::DirectoryOnly);
  QStringList download_location(QStandardPaths::standardLocations(QStandardPaths::DownloadLocation));
  file_dialog->exec();
}

Code:

cmake_minimum_required(VERSION 3.5)
project(hidpi_test)
add_compile_options(-Wall -Wextra)
set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
## Find Qt5
set(CMAKE_AUTOMOC ON)
find_package(Qt5Widgets REQUIRED)
 
add_executable(
  ${PROJECT_NAME}
  mainwindow.hpp
  mainwindow.cpp
  main.cpp
)
target_link_libraries(
  ${PROJECT_NAME}
  Qt5::Widgets
)

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.

Attachment 13739 Attachment 13740

How can I get all the icons right?