Install Element (formerly Riot) on Debian, Ubuntu or derivatives

All at once:

sudo wget -O /usr/share/keyrings/element-io-archive-keyring.gpg \
          https://packages.element.io/debian/element-io-archive-keyring.gpg

echo "deb [signed-by=/usr/share/keyrings/element-io-archive-keyring.gpg] https://packages.element.io/debian/ default main" \
| sudo tee /etc/apt/sources.list.d/element-io.list

sudo apt update
sudo apt install element-desktop

Step-by-step:

1. Import Element repository signature key:

   sudo wget -O /usr/share/keyrings/element-io-archive-keyring.gpg https://packages.element.io/debian/element-io-archive-keyring.gpg
   

2. Add Element repository to your system:

   echo "deb [signed-by=/usr/share/keyrings/element-io-archive-keyring.gpg] https://packages.element.io/debian/ default main" | sudo tee /etc/apt/sources.list.d/element-io.list
   

3. Update repositories database and install Element:

   sudo apt update; sudo apt install element-desktop
   

Source: element.io