Upgrading Inspiron 660 to Windows 11

Short answer

No, you can't reasonably run Windows 11. You should install Windows 10.

Longer answer

Your PC is ten years old. It does not meet the requirements for Windows 11. It has only a 3rd-gen CPU, lacks TPM and Secure Boot, etc.

While there are ways to get around Microsoft's minimum requirements, you would face two issues:

• Microsoft has stated that at some point they may enforce the requirements so that systems that don't meet the requirements would no longer receive updates for Windows 11.
• Windows 11 is likely to perform poorly on your old system.

Windows 8.1 will be end-of-life in two weeks, at which point it will be unsupported and insecure. It will not receive security patches, so it should no longer be used on a PC connected to the Internet.

I suggest that you update to Windows 10, which should run well on your system. Do the free upgrade: https://www.zdnet.com/article/heres-how-you-can-still-get-a-free-windows-10-upgrade/

After upgrading, check to see if Windows 10 is activated in Settings | Activation. If it is, then you can perform a clean install of Windows 10 and it should activate automatically.