How can I set a custom CKEditor on only one field? I'm using Drupal 8.

I have a field that can only allow for specific styles, so I created a custom CKEditor and set the field to use it.

Now when I go to the field on the content edit form, I see the custom editor as the default, as well as a select menu to specify which editor I want to use to enter content.

When editing this field, I do not want to show any other editor options and I only want the editor to be used for this field.

What is the best way to implement this functionality?
I believe the module you want to add is Better Formats. This will let you specify format options for a field, if you only want to show one (even if the role has access to multiple).

Edit, because it is not clear from the project page:

composer require drupal/better_formats:1.x-dev