At my last client, we had a PMO driving improvement of the project portfolio in terms of efficiency, capacity, and quality for about 400 projects, of which about 40 were considered significant. Integration of projects and agile teams was required. We considered it a transformation, yet there was no defined target state.
In parallel, one of the portfolio components was a massive transformation to drive the digitization of the (manufacturing) organization, for which a separate PMO was needed. Also here the end state was not fixed.
So, there is not only one transformation in an organization, and they are often open-ended. PMOs support a specific scope; there can be many. Alignment between them is necessary.