32-bit OS only available in virtualbox-6.0/5.2 on 64-bit Ubuntu 18.04 LTS host?

Hello,

I installed a .deb package virtualbox-6.0 (amd64) from Virtualbox Linux_Downloads on Ubuntu Mate 18.04.1 Bionic 64-bit host (HP notebook)
and noticed that for new Windows and Linux guests there are only 32-bit versions available. The same 32-bit guest versions only were available
also after installing virtualbox-5.2 on the same host via Software Boutique.

I have also an Ubuntu Mate 16.04 LTS 64-bit host installed earlier on an Asus notebook and an Oracle virtualbox v. 5.2.18 (r124319 Qt5.6.1)
installed there which allows 64-bit Windows and Linux guests to be created. A Windows 8.1 64-bit guest was successfully created and used there.

What's the issue of only 32-bit guests available to create in amd64 vIrtualbox on Ubuntu 18.04.1 64-bit host? Is it possible to enable Virtualbox
with the option for 64-bit Linux and Windows guests?
(I basically need at least a one 64-bit Windows (8 preferentially) guest).

Can there be any danger of installing virtualbox for 64-bit Ubuntu 16.04 Xenial (which seems to allow 64-bit guests) onto 64-bit Ubuntu 18.04 host?


Thanks