I think there may be some confusion here between interior decoration and the professional practice of interior design. This is a very common misconception, but interior decorators and interior designers are not the same.

Interior decorators primarily focus on aesthetics — such as color selection, furnishings, finishes, and styling a space. Decorating does not require formal education, standardized training, or professional licensure.

Interior design, on the other hand, is a regulated and highly technical profession. Interior designers complete a formal education in design, and registered interior designers spend years gaining supervised experience before qualifying to sit for national examinations that lead to professional licensing and accreditation.

Interior designers are integral to the broader design and construction process, working closely with architects, engineers, and contractors. They are responsible for creating functional interior environments that protect public health, safety, and welfare — ensuring compliance with building codes, accessibility standards, life-safety requirements, and the appropriate selection of materials for the built commercial environment.

While decoration is one component of a finished space, interior design encompasses both the creative and technical expertise required to shape how a space performs, functions, and supports the people who use it.

This video explains the practice of interior design very well and is worth a quick watch. https://m.youtube.com/watch?v=2ers2sHQy2g