تحفة الأخيار ببيان جملة نافعة مما ورد في الكتاب والسنة - ابن باز

Windows: Run the installer and follow the steps. If SmartScreen warns that the app is not signed with a developer certificate, choose More info, then Run anyway.

Mac: Open the DMG and drag Aljam3 into Applications, then open it from there. If macOS blocks it because it is not notarized by Apple, go to System Settings → Privacy & Security and choose Open Anyway.