DIAGNOSIS The default interface is ad-supported. You cannot fully remove all promoted content from the Google TV home screen. It is part of the OS design.
FIX You can customize some rows. On the home screen, navigate to a row like 'For you'. Press the select button to open the row options. Select 'Customize row'. Here you can sometimes remove specific channels or apps from that row's suggestions.
IF THAT DIDN'T WORK Install a third-party launcher like 'Sideload Channel Launcher 3' or 'Projectivy'. This requires enabling Developer Options and 'Unknown Sources' to install an APK. The new launcher will replace the default home screen interface.
HEADS UP Using a third-party launcher is not officially supported. Some app buttons on the remote may not function correctly. You may need to use a 'Launcher Manager' app to set the default.