Proximity-induced superconductivity in strongly correlated insulators provides a versatile route for engineering quantum states and artificial systems with tailored functionalities. Yet microscopic interplay between superconductivity and correlated insulating states remains poorly understood. Here we use scanning tunnelling microscopy (STM) to investigate superconducting proximity effects in a charge-transfer insulator. Via STM tip manipulation, atomically sharp lateral junctions composed of superconducting monolayer H-NbSe2 and charge-transfer insulating monolayer T-NbSe2 are constructed, enabling direct access to tunable coupling regimes. In weak-coupling regime, there is a robust proximity-induced superconducting gap in T-NbSe2, with a reduced gap relative to that of H-NbSe2. Upon entering strong-coupling regime, T-NbSe2 exhibits a superconducting gap comparable to that of H-NbSe2, accompanied by pronounced in-gap bound states, consistent with Yu-Shiba-Rusinov-like excitations. These findings establish H/T-NbSe2 lateral junctions as a model platform for elucidating superconducting proximity effects in strongly correlated charge-transfer insulators.