In order to access full resolution inside your VM and to access USB Devices with full USB3 Speed you need to install Virtual Box Extensions:
Go to https://download.virtualbox.org/virtualbox and select the appropriate version. Then download the extension pack, e.g. Oracle_VM_VirtualBox_Extension_Pack-6.1.12.vbox-extpack
Then open VirtualBox >> Preference >> Extensions >> browse for extension pack by clicking on the + icon.
Click on the install button and choose the file.
To access you usb devices you also need to add your user to group vboxusers
sudo usermod -aG vboxusers <user>
