Defender will continue to provide security even for unsupported Windows 10 PCs. But Microsoft still wants you to move to Windows 11.
If you’re thinking about moving forward, Microsoft recommends checking if your PC can run Windows 11. You can do this through the PC Health Check app or by going to Settings > Windows Update.
Microsoft ends support for Windows 10. After that, systems running Windows 10 will no longer receive security patches, bug fixes, or official support.  ...