Dr. Xiaopeng Cheng is a Brain Pool Invited Researcher at the Korea Astronomy and Space Science Institute (KASI). He received his PhD from Shanghai Astronomical Observatory (SHAO) in 2019 and has been working at KASI since then. His research interest is primarily high angular resolution imaging and astrometric studies of supermassive black holes (SMBH) and active galactic nuclei (AGN). His recent work includes long-term EAVN monitoring of Sagittarius A*, microarcsecond astrometric study of the binary black hole candidate OJ 287, and the first discovery of a unique jet in the nearly dormant SMBH M60*. He is an active member of the EHT Collaboration, EAVN, and the SKA-VLBI Working Group.Most galaxies host supermassive black holes that spend most of their lifetimes in a weakly accreting or dormant state. At the lowest accretion rates, whether these systems can still launch collimated jets remains an open question. Sagittarius A*, the supermassive black hole at the center of our Galaxy, is one of the best laboratories for studying this regime, although strong interstellar scattering makes direct jet detection challenging. In this talk, I will present a series of VLBI studies aimed at understanding black hole activity at extremely low accretion rates. I will first discuss long-term EAVN monitoring observations of Sagittarius A*, including its variability and possible multi-year activity cycle. I will then introduce a high-resolution VLBI survey of nearby low-luminosity AGN designed to search for compact radio cores and weak jets. Finally, I will present recent multi-frequency VLBI observations of M60*, one of the best extragalactic analogs of Sagittarius A*. The discovery of a compact two-sided jet and a significant core shift in M60* provides direct evidence that jet activity can survive even in nearly dormant black holes, suggesting that weak jets may be more common than previously thought.