diff --git a/scanslicer/entry.py b/scanslicer/entry.py
index 997ecd7..f38d69e 100644
--- a/scanslicer/entry.py
+++ b/scanslicer/entry.py
@@ -63,3 +63,37 @@ def resolve_runtime_backend(backend):
 
     # Fall back to Wayland when auto-detection has no clear signal.
     return "wayland"
+
+
+# configure_qt_backend: function definition for ScanSlicer behavior.
+def configure_qt_backend(backend):
+    if backend == "wayland":
+        os.environ["QT_QPA_PLATFORM"] = "wayland"
+        # Prevent accidental X11/XWayland routing in mixed environments.
+        os.environ.pop("DISPLAY", None)
+    elif backend == "x11":
+        os.environ["QT_QPA_PLATFORM"] = "xcb"
+    else:
+        raise RuntimeError(f"Unsupported backend '{backend}'.")
+
+    is_appimage = bool(os.environ.get("APPIMAGE"))
+
+    # In sandboxed desktop runtimes (Flatpak/Snap), prefer portal integration
+    # for file dialogs and desktop services.
+    sandboxed = bool(
+        os.environ.get("FLATPAK_ID")
+        or os.environ.get("SNAP")
+    )
+    if sandboxed:
+        os.environ.setdefault("QT_QPA_PLATFORMTHEME", "xdgdesktopportal")
+    elif is_appimage:
+        # AppImage is not a strict sandbox and some portal backends can emit:
+        # "Connection already associated with an application ID".
+        # Prefer GTK theme integration and avoid forced portal registration.
+        os.environ.setdefault("QT_QPA_PLATFORMTHEME", "gtk3")
+        os.environ.setdefault("QT_NO_XDG_DESKTOP_PORTAL", "1")
+
+    # In containers, prefer GTK platform theme so Qt can follow host theme
+    # settings when available (for example dark/light mode).
+    if os.path.exists("/.dockerenv"):
+        os.environ.setdefault("QT_QPA_PLATFORMTHEME", "gtk3")