I was curious why I could not use 64-bit guest operating systems on my Ryzen 4 machine. Turned out, there was a setting that got disabled by default. It is called the Secure Virtual Machine (SVM).
I rebooted my machine, went into the BIOS. Specifically for the ASRock AB350M PRO4 motherboard, navigate to the Advanced, then go to the CPU Configuration, and you can now enable the SVM mode.
It was disabled by default
Now I can run 64-bit guest OS through the Virtualbox. No need to re-install the Virtualbox. Now I am really curious why this feature is disabled by default.