To deactivate it, follow the steps below:
- Sign in as Drupal administrator,
- Go to Structure, then Block layout
- Find the Site branding block and on the right-hand side, click on Configure
- In the next page deactivate the Site name by unchecking the corresponding checkbox
- Click save
There's a video version of how to disable the site name on a Drupal site.
Browse back to the homepage of your Drupal 8 site to see the change reflected.
The same process applies to the following Site branding elements:
- Site Logo
- Site Slogan