As I understand it, the point is that land rent is a large and stable rent, where taxing it has few supply-side side-effects, not that land rent is the only rent.

The second paragraph of the Georgism Wikipedia page mentions other rents,

> Georgism is concerned with the distribution of economic rent caused by land ownership, natural monopolies, pollution rights, and control of the commons, including title of ownership for natural resources and other contrived privileges (e.g., intellectual property).

https://en.wikipedia.org/wiki/Georgism