When creating a new field, if an app builder does not want the field to be automatically added to pre-existing custom report types, the step to take is:
Deselect 'Add Field to Custom Report Types' (D). This option is available when creating or editing a custom field and ensures that the field is not automatically included in report types where 'Automatically add new custom fields to report type layouts' is enabled.
Removing the field from page layouts (A) affects the visibility on record pages but not reports. Adjusting visibility (B) or setting read-only access (C) for report profiles affects user permissions to see the field in reports, but does not remove the field from report types if it was previously added.
Reference for managing fields in custom report types:
Custom Report Types and Fields: https://help.salesforce.com/articleView?id=reports_report_type_layouts.htm&type=5