Allowing only 1 block?

Is there any way to disable the ability to add new blocks?

The way I use this editor is that the content is already present and only use a modified list module.

I need to somehow disable the ability to add new blocks and allow only editing the one existing block.

The issue names no files, tests, or entry points. Start by locating the editor's block-creation controls and how a single existing block is configured; done means the existing block remains editable while attempts to add new blocks are prevented.

Written by the indexing model from the issue text.