It was showing 64-bit operating systems as one of those options in VirtualBox but you don’t know why there are only 32-bit versions listed below. There are two issues here. You either have Hyper-V turned on, or have Intel Virtualization Technology disabled in BIOS. Website:: https://www.facebook.com/TheProgrammingPortal/. I have downloaded and installed the newest virtualbox 4.3.20 for my Windows 7 (64-bit OS), but when I want to install 64-bit Linux, the New-Create Virtual Machine only displays 32-bit option, no 6. Go to the system configuration tab. You will find visualization technology as disabled. Turn it Enabled. Select virtualization technology row and press enter. Press F10 to save the changes and exit. Now I am able to select ubuntu 64 bit when I create VirtualBox. VirtualBox Showing Only 32-bit Guest Versions on 64-bit Windows 10 - 2019.
When trying to create a Virtualbox VM recently I was only presented with the option of creating a 32-bit client. After a bit of research it turns out this can be caused by incorrect settings in the BIOS or by a competing Virtual Machine software cohabiting the system.
CPU
First of all your CPU must support the virtualization extensions. We can check this on a Bash console if you have installed the integrated feature.
If it returns a positive number, 1 or higher your CPU does support the virtualization extensions. You must still ensure it's enabled in the BIOS. If it returns 0 then your CPU does not support hardware virtualization.
BIOS
You must have hardware virutalization enabled in the BIOS to create and run 64-bit virtual machines.
The following BIOS features need to be enabled:

Hyper-V
If Hyper-V is enabled then Virtualbox will not be able to create 64-bit virtual machines.
If Hyper-V was enabled this will require a reboot.
References