On Linux Mint 20 (based on Ubuntu Focal)
# add the official repository
echo "deb [arch=amd64] https://download.virtualbox.org/virtualbox/debian focal contrib" | sudo tee /etc/apt/sources.list.d/virtualbox.list
# add the key
wget -q https://www.virtualbox.org/download/oracle_vbox_2016.asc -O- | sudo apt-key add -
# install it
sudo apt update && sudo apt install -y virtualbox-6.1
# just confirming
sudo systemctl status vboxdrv
What to do when experiencing The following signatures were invalid BADSIG:
sudo -s -H
apt-get clean
rm /var/lib/apt/lists/*
rm /var/lib/apt/lists/partial/*
apt-get clean
apt-get update