Optical interferometry has been used to synthesize very large apertures in ground based experiments (e.g., https://en.wikipedia.org/wiki/Palomar_Testbed_Interferometer). That was in the mid 1990s.

Operational ground interferometers have obtained 5 mas resolution, which corresponds to sub-mm resolution from an orbital platform.

You still have atmospheric turbulence, but do we know how to get around the naive diffraction limit.