Make Qt 6 builds use a custom profile instead of the QtWebEngine defaultProfile. In Qt 6, defaultProfile is off-the-record which means every session would behave like private/incognito mode.

src/lib/app/mainapplication.cpp

@@ -298,7 +298,11 @@ MainApplication::MainApplication(int &argc, char** argv)
     NetworkManager::registerSchemes();
     registerAllowedSchemes();
 
+#if (QT_VERSION < QT_VERSION_CHECK(6, 0, 0))
     m_webProfile = isPrivate() ? new QWebEngineProfile() : QWebEngineProfile::defaultProfile();
+#else
+    m_webProfile = isPrivate() ? new QWebEngineProfile() : new QWebEngineProfile(QSL("Default"));
+#endif
     connect(m_webProfile, &QWebEngineProfile::downloadRequested, this, &MainApplication::downloadRequested);
 
     m_webProfile->setNotificationPresenter([&] (std::unique_ptr<QWebEngineNotification> notification) {
@@ -404,6 +408,12 @@ MainApplication::~MainApplication()
     delete m_cookieJar;
     m_cookieJar = nullptr;
 
+#if (QT_VERSION >= QT_VERSION_CHECK(6, 0, 0))
+    // On Qt 6, deleting the web profile is necessary in order to make sure cache, cookies, etc. are flushed to disk.
+    delete m_webProfile;
+    m_webProfile = nullptr;
+#endif
+
     Settings::syncSettings();
 }
 
@@ -1006,7 +1016,11 @@ void MainApplication::loadSettings()
     webSettings->setFontSize(QWebEngineSettings::MinimumLogicalFontSize, settings.value(QSL("MinimumLogicalFontSize"), 5).toInt());
     settings.endGroup();
 
+#if (QT_VERSION < QT_VERSION_CHECK(6, 0, 0))
     QWebEngineProfile* profile = QWebEngineProfile::defaultProfile();
+#else
+    QWebEngineProfile* profile = m_webProfile;
+#endif
     profile->setPersistentCookiesPolicy(QWebEngineProfile::AllowPersistentCookies);
     profile->setPersistentStoragePath(DataPaths::currentProfilePath());
 

src/lib/other/useragentmanager.cpp

@@ -19,6 +19,7 @@
 #include "browserwindow.h"
 #include "qztools.h"
 #include "settings.h"
+#include "mainapplication.h"
 
 #include <QWebEngineProfile>
 #include <QRegularExpression>
@@ -27,7 +28,7 @@ UserAgentManager::UserAgentManager(QObject* parent)
     : QObject(parent)
     , m_usePerDomainUserAgent(false)
 {
-    m_defaultUserAgent = QWebEngineProfile::defaultProfile()->httpUserAgent();
+    m_defaultUserAgent = mApp->webProfile()->httpUserAgent();
     m_defaultUserAgent.replace(QRegularExpression(QSL("(QtWebEngine/[^\\s]+)")), QSL("Falkon/%1 \\1").arg(Qz::VERSION));
 }
 
@@ -53,7 +54,7 @@ void UserAgentManager::loadSettings()
     }
 
     const QString userAgent = m_globalUserAgent.isEmpty() ? m_defaultUserAgent : m_globalUserAgent;
-    QWebEngineProfile::defaultProfile()->setHttpUserAgent(userAgent);
+    mApp->webProfile()->setHttpUserAgent(userAgent);
 }
 
 QString UserAgentManager::globalUserAgent() const

src/lib/preferences/preferences.cpp

@@ -310,7 +310,7 @@ Preferences::Preferences(BrowserWindow* window)
     ui->allowCache->setChecked(settings.value("AllowLocalCache", true).toBool());
     ui->removeCache->setChecked(settings.value("deleteCacheOnClose", false).toBool());
     ui->cacheMB->setValue(settings.value("LocalCacheSize", 50).toInt());
-    ui->cachePath->setText(settings.value("CachePath", QWebEngineProfile::defaultProfile()->cachePath()).toString());
+    ui->cachePath->setText(settings.value("CachePath", mApp->webProfile()->cachePath()).toString());
     connect(ui->allowCache, &QAbstractButton::clicked, this, &Preferences::allowCacheChanged);
     connect(ui->changeCachePath, &QAbstractButton::clicked, this, &Preferences::changeCachePathClicked);
     allowCacheChanged(ui->allowCache->isChecked());