I’m planning to redo the course again but this time by using hyper v because virtualbox new version of 7.0 or above no longer has network option in preferences for NatNetwork for adding CIDR that I couldn’t find. Also, because of the past problems with using virtualbox when doing the labs, I’m going to try using hyper v to see if it has less problems than using virtualbox. Also, Microsoft no longer supports internet explorer therefore, I’m going to download google chrome application before attempt to install to install sccm 1902 on hyper v.
Let us know how it goes. Nice way of learning everything Microsoft. 
I have also experienced some issues on VirtualBox 7 on Ubuntu with Networking in general. I am not sure what the problem is, but it seems that sometimes it works, and sometimes it does not. I have tried in the past with VMware Workstation, and when upgrading the Kernel on Ubuntu, the VMware Workstation needed to be recompiled. I’ll keep troubleshooting VirtualBox for now 
Ricardo