What aspect of receiver analog-to-digital conversion determines the maximum receive bandwidth of a direct-sampling software defined radio (SDR)?

The Nyquist-Shannon sampling theorem dictates that in order to accurately capture and digitize a signal of a certain bandwidth, the sample rate must be at least twice the highest frequency of that bandwidth. Therefore, the absolute maximum receive bandwidth of a direct-sampling SDR is fundamentally limited and determined by how fast it takes those samples (the sample rate). Other characteristics of the ADC dictate different performance metrics. For example, the sample width in bits (often called bit depth) is crucial for determining the receiver's dynamic range—the difference between the strongest and weakest detectable signals—but it plays no role in determining frequency bandwidth.