Effects of anharmonic phonons on superconductivity in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:math> -intercalated boron-carbon clathrate <mml:math xmlns:mml="ht

Achieving structural stability and high critical temperature $({T}_{c})$ in hydrides under ambient conditions remains a major challenge. A feasible design strategy integrates the advantages of two material classes: (i) B-C--based clathrate superconductors, which exhibit excellent structural stability at ambient or relatively low pressures, and (ii) hydrogen-based unit, which possesses the potential for high ${T}_{c}$. Guided by this strategy, we theoretically predict a hypothetical compound ${\mathrm{NH}}_{4}{\mathrm{B}}_{2}{\mathrm{C}}_{8}$ by embedding hydrogenated units into a B-C clathrate framework. Using the stochastic self-consistent harmonic approximation combined with machine-learning-accelerated structural sampling, we assess the impact of anharmonicity on its superconducting properties. Anharmonic effects harden the dominant phonon modes 13--15, reducing the electron-phonon coupling constant $\ensuremath{\lambda}$ from 1.43 to 1.22 and lowering ${T}_{\text{c}}$ from 102 to 91 K. Furthermore, hole doping realized by ${\mathrm{NH}}_{4}$ vacancy engineering, which yields ${({\text{NH}}_{4})}_{3}{({\text{B}}_{2}{\text{C}}_{8})}_{4}$, is demonstrated to be ineffective in enhancing ${T}_{c}$ under anharmonic conditions. Our results highlight the synergistic role between hydrogen units and B-C frameworks in enhancing superconductivity, and underscore the importance of anharmonicity in the design of such superconductors.