Shutdown your VM and do:
VirtualBox > Settings > Network > Add (you will get vboxnet0)
On a terminal ifconfig will show you new interface vboxnet0
VM's Settings > System > check "Enable I/O APIC." VM's Settings > Network > Adapter 2 > host-only vboxnet0
Install OpenSSH Server
Edit /etc/network/interfaces file to append the following lines:
auto eth1
iface eth1 inet static
address 192.168.56.10
netmask 255.255.255.0
Run sudo ifup eth1 from the Ubuntu command line.
SSH server should be up and running. Switch to your host terminal and enter ssh 192.168.56.10
sources:
VirtualBox UI had been redesigned, the UI for step #1 had been moved to File > Host Network Manager.
I'm not sure which version this change was introduced into, perhaps long time ago? I'm on v6.1.16 for MacOS.