Your system has an older CPU, gen 6, which is officially not compatible with Windows 11. Dell therefor does not offer drivers for Windows 11 on the 7559. However you can update to Windows 11 by downloading the Windows 11 media creation tool here which will create a bootable Windows 11 installation flash drive. The process is exactly like the Windows 10 procedure. Just be sure to click on the Create Windows 11 Installation Media choice. That procedure will bypass the CPU checks. Google search on installing Windows 11 unsupported hardware and you will find many how to articles such as these at YouTube.

Keep in mind though that if you need Dell service down the road, Dell tech support will insist that you reinstall your original OS before they will assist you.

@JOcean​ When I try to upgrade to Windows 11 that my Optiplex 7040 does not meet the requirements.

@Bob Lawrence​ If you follow my links and go to YouTube there are a number of methods for installing Windows 11 on unsupported hardware. I have Windows 11 on a 3rd Gen laptop and a 6th Gen desktop and they run perfectly fine.