Today I received the Samsung EVO 870 SSD hard disk that I ordered, and on Monday I will receive a Windows 10 that I ordered from the Microsoft Store.
I will take the opportunity to change my current Windows 7, for a Windows 10, and install both Linux Ubuntu and Windows 10 on the same SSD. I don't have the Windows 10 yet, so I'll install Ubuntu now and rerun the whole buildroot compilation process for Raspberry pi3 and 4.
All of the above (VirtualBox in W7 with Linux, buildroot compiled in Raspberry pi4) I already tried it and it did not work, also when I enabled virtualization in the BIOS to be able to create a 64bit Linux in VirtualBox it disabled the Windows7 license, and it did not work either VirtualBox, it gave me an error. I no longer waste time with those things, now I will work directly on Linux.
I have insisted on working with buildroot, because I have read of people who have achieved versions that boots even in less than 2 seconds, perfect for embedded applications. And from what I was seeing in the buildroot configuration menu there are a lot of options that allow you to create a custom linux only with what you need for the Raspberry. There are preconfigured configuration files for Raspberry 3 and 4, 32 and 64 bit, pretty much the only thing I modified was to include ssh and wifi then run the compilation with make, very easy.