If you take a look at the manifest schema for a SPFx web part there are a couple of settings you might want to take a look at.
hiddenFromToolbox
If hiddenFromToolbox is set to "true", the web part will not be visible in the modern SharePoint toolbox. Very useful for web parts you provision automatically on pages, but don’t want users to add themselves.
supportsFullBleed
If supportsFullBleed is set to "true", the web part can be added to a full page width zone on a modern page in a communication site, spanning from the left margin to the right margin without any white space.
