Since WordPress update 5.0+ the new Gutenberg editor is enabled and launch button of Visual Builder is not visible. We will get our button back in the nearest update of Content Editor plugin. As a temporary solution you may find Visual Builder link at the top admin bar while viewing page or post on front-end.
Or you may find Visual Builder link that launches Content Editor while viewing list of pages or posts in your dashboard.
You may also temporary disable Gutenberg editor to get the launch button back by installing and activating Classic Editor plugin.