In interferometry [0], you need your telescope components to be collecting data simultaneously so that you can interfere their collected light together - so the maximum possible separation is about the diameter of the Earth. (The VLBA [1] and the EHT [2] make use of most of this potential.)
There have been proposals to extend this maximum baseline by having space-borne interferometers (perhaps orbiting the Sun), but practically, they are a few decades away at best. [3]