According to wikipedia the NX is ...
The NX bit (no-execute) is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions (code) or for storage of data, a feature normally only found in Harvard architecture processors. However, the NX bit is being increasingly used in conventional von Neumann architecture processors for security reasons.
An operating system with support for the NX bit may mark certain areas of memory as non-executable. The processor will then refuse to execute any code residing in these areas of memory. The general technique, known as executable space protection, is used to prevent certain types of malicious software from taking over computers by inserting their code into another program's data storage area and running their own code from within this section; one class of such attacks is known as the buffer overflow attack.
Intel markets the feature as the XD bit (execute disable). Advanced Micro Devices (AMD) uses the marketing term Enhanced Virus Protection (EVP). The ARM architecture refers to the feature, which was introduced in ARMv6, as XN (execute never). The term NX bit itself is sometimes used to describe similar technologies in other processors.
Solution is easy.
This problem mostly occured on 32bit system regardless what type of your CPU.
To let it clear you can run 32bit Windows on 64bit CPU but you can't run 64bit Windows on 32bit CPU.
Currently in 2020 you had to have a very old PC to have 32bit only CPU in normal case, thats good because possibly you have a 64bit CPU.
I recommend to only upgrade to Windows 10 when you have at least 4GB RAM and 40GB free space.
If you want to upgrade because Windows 10 maybe faster than Windows 7, nope. Windows 10 eats more resources.
If you have enough RAM but your PC is a damn slow, switch to SSD then upgrade, this is cheap and very effective speed-up to your machine.
Now let's facing to resolv the issue, all you need:
Open Command Prompt as System Administrator privileges, search for cmd.exe and right-click run as System Administrator.
Now we assume a black box appeared like MS-DOS, you have to type:
bcdedit.exe /set nx AlwaysOn
Reboot your machine, start upgrade and enjoy.