If you cannot afford Windows, run it unactivated (it never expires, just nags you) or use Linux. Do not risk your security for a free key.
Here are some common issues that users may encounter with their Microsoft Windows 10 64 bit product key: microsoft windows 10 64 bit product key
If you buy a Windows 10 key now, you can still upgrade to Windows 11 for free in the future. A Windows 10 key activates Windows 11 on compatible hardware. So, buying a Windows 10 key is not a waste—it gives you flexibility. If you cannot afford Windows, run it unactivated