Go to this site: https://www.synaptics.com/products/displaylink-graphics/downloads/ubuntu (or follow the instructoin on that site)
- wget https://www.synaptics.com/sites/default/files/Ubuntu/pool/stable/main/all/synaptics-repository-keyring.deb
- sudo apt install synaptics-repository-keyring.deb
- sudo apt update
- sudo apt install displaylink-driver