I just tested a simple Qt app on my Linux KDE Neon and it consumes just ~32.3 MB RSS. Simple Qml app memory consumption is ~120.4 MB RSS.

$ ps -o pid,rss,command -p $(pgrep -f SimpleQtApp)

PID RSS COMMAND

1471929 33052 ./SimpleQtApp

$ ps -o pid,rss,command -p $(pgrep -f SimpleQmlApp)

PID RSS COMMAND

1478335 123260 ./SimpleQmlApp

// Following is the simple Qt app code.

#include <QApplication>

#include <QWidget>

#include <QLabel>

#include <QPushButton>

#include <QVBoxLayout>

int main(int argc, char argv[]) {

    QApplication app(argc, argv);
    QWidget window;
    window.setWindowTitle("Qt Simple App (CMake)");
    window.resize(300, 150);

    QLabel *label = new QLabel("Hello, World!", &window);
    label->setAlignment(Qt::AlignCenter);

    QPushButton *button = new QPushButton("Click Me", &window);

    QVBoxLayout *layout = new QVBoxLayout(&window);
    layout->addWidget(label);
    layout->addWidget(button);

    QObject::connect(button, &QPushButton::clicked, [label]() {
        label->setText("You clicked the button!");
    });

    window.show();
    return app.exec();

// Following is the QML app code

#include <QGuiApplication>

#include <QQmlApplicationEngine>

int main(int argc, char *argv[]) {

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    const QUrl url(QStringLiteral("qrc:/Main.qml"));

    QObject::connect(&engine, &QQmlApplicationEngine::objectCreationFailed, &app, []() { QCoreApplication::exit(-1); }, Qt::QueuedConnection);

    engine.load(url);

    return app.exec();

// Main.qml

import QtQuick

import QtQuick.Controls

Window {

    width: 320
    height: 200
    visible: true
    title: "Simple QML Application"

    Column {
        anchors.centerIn: parent
        spacing: 20

        Label {
            id: statusLabel
            text: "Hello, QML World!"
            font.pointSize: 16
            anchors.horizontalCenter: parent.horizontalCenter
        }

        Button {
            text: "Click Me"
            anchors.horizontalCenter: parent.horizontalCenter
            
            // Handle click event inline
            onClicked: {
                statusLabel.text = "You clicked the QML button!"
            }
        }
    }
}

Sure. Sorry it wasn't clear; I meant I just tested the Telegram desktop app for Linux.