Author clicks the Install All updates in WordPress 5.0 and after a few seconds the user gets the WSOD error page with the link to debugging in Wordpress.
SSH to server with the Authors remote SSH credentials.
Navigate to the appropriate web folder, edit the wp-config.php, and update the WP_DEBUG is true.
e.g. /var/www/authorblogsite.com/web or just /web
$ cd /web
$ vi wp-config.php
Return the web browser and see the exact error message:
Fatal error: Cannot declare class WP_REST_Blocks_Controller, because the name is already in use in /var/www/clients/client23/web20/web/wp-content/plugins/gutenberg/lib/class-wp-rest-blocks-controller.php on line 0
There has been a critical error on your website.
$ cd wp-content/plugins/
$ ls -l
Remove the plugin folder (or move it out of the wp-content/plugins folder so WordPress engine cannot find it.
$ rm -rf gutenberg
Return to the web browser and try the site again. It should load just fine now.
Add the wp-admin path, and confirm you can edit a blog page okay. Since the gutenberg plugin was related to blocks, editing a page of blocks will confirm the WP built-in editor is working well.
Since the problem was duplicate name in use error, this indicates that there are two plugins doing the same code. Or in this case, WordPress now has gutenberg INSIDE itself, and no longer needs this plugin. Yes, the WP upgrade should check this first.