Have you even written an original essay, article, or research thesis? Those thoughts are entirely of your creation or finding from evidence as well as the organization thereof. Original software is no different in that you are writing both the solutions and the architecture.
It sounds like this originality should be slow and of great challenge. It isn’t. With practice the words just appear in the correct order as fast as they are typed.
In the overwhelming majority of full stack jobs that level of originality does not exist. Most of these jobs, and the developers filling them, are utterly reliant upon large tool sets of prior formulated architectures. These large frameworks rob the developers of the practice necessary to become faster in their solution delivery and cripple their ability to consider answers of their own design.
As an example consider state management. That is an astonishingly simple problem to solve, essentially saving a result of modification for later artifact generation. With these large frameworks, however, the solution becomes a complex science to compensate for modularity considerations introduced by the frameworks that do not otherwise exist. For developers that have never written an original application without one of these large frameworks the simplicity of the solution is almost impossible to fathom, thus resulting in solutions of complexity outside their control and no ability for consideration of alternatives.