The fact is that the system requirements for Windows 11 and Windows 10 don’t differ much, but slight differences can easily mean that you can’t upgrade your machine to the new system. If you want to check that your device meets the requirements of Windows 11, PC Health Check is one of the best and indeed the only official application for the job.
Although it is worth using this program, it does not tell you what the specific problem is in the event of a negative answer; however, as Microsoft makes the app, if it gives the green light, you should have no issues running Windows 11.
If you answer that the machine is not running Windows 11, you can use the Why-NotWin11 program to find out exactly which component or what is missing. If the answer is no, the most common causes are the lack of Secure Boot, the wrong version of TPM, the complete lack of TPM, or an incompatible processor.