To add a repository for your architecture use [arch=amd64]
sudo add-apt-repository 'deb [arch=amd64] https://download.virtualbox.org/virtualbox/debian bionic contrib'
To add a repository for your architecture use [arch=amd64]
sudo add-apt-repository 'deb [arch=amd64] https://download.virtualbox.org/virtualbox/debian bionic contrib'