The silicon vacancy (VSi) in 4H-SiC is a room temperature single-photon emitter with a controllable high-spin ground state and is a promising candidate for future quantum technologies. However, controlled defect formation remains a challenge, and, recently, it was shown that common formation methods such as proton irradiation may, in fact, lower the intensity of photoluminescence (PL) emission from VSi as compared to other ion species. Herein, we combine hybrid density functional calculations and PL studies of the proton-irradiated n-type 4H-SiC material to explore the energetics and stability of hydrogen-related defects, situated both interstitially and in defect complexes with VSi, and confirm the stability of hydrogen in different interstitial and substitutional configurations. Indeed, VSi-H is energetically favorable if VSi is already present in the material, e.g., following irradiation or ion implantation. We demonstrate that hydrogen has a significant impact on electrical and optical properties of VSi, by altering the charge states suitable for quantum technology applications, and provide an estimate for the shift in thermodynamic transition levels. Furthermore, by correlating the theoretical predictions with PL measurements of 4H-SiC samples irradiated by protons at high (400 C) and room temperatures, we associate the observed quenching of VSi emission in the case of high-temperature and high-fluence proton irradiation with the increased mobility of Hi, which may initiate VSi-H complex formation at temperatures above 400 C. The important implication of hydrogen being present is that it obstructs the formation of reliable and efficient single-photon emitters based on silicon vacancy defects in 4H-SiC.