To install an SDDM theme on Linux, follow these steps:1. Download an SDDM theme from the Pling website.2. Extract the theme content using the file explorer or terminal.3. Move the theme folder to /usr/share/sddm/themes/.4. Edit the SDDM configuration file at /etc/sddm.conf.5. Restart the SDDM service using 'sudo systemctl restart sddm.service'.