Sub-THz frequencies are tomorrow’s hot research area in mobile communication. However, in this range of frequencies the systems are complex, and it is hard to explore various system architectures and correlate the system-level solutions with circuit-level performances and requirements. This paper presents a scalable testbench in MATLAB/Simulink for sub-THz hybrid beamforming receivers. The testbench models analog and mixed signal blocks with high fidelity, enabling system level simulations with circuit-level imperfections. A receiver with multiple 4-element subarrays is simulated in the testbench, and the impact of phase noise, beam squint, phase shifter inaccuracies, ADC resolution, and more are investigated. Additionally, a Mueller-Müller symbol synchronizer is implemented to achieve symbol-rate sampling.