At least on the C172 with the steam gauges, the Bendix King KMA-26 is a softkey solution.
In theory, if the ATIS is on COM2, (and the led is showing COM2 as RX Monitoring), just click on the button to deselect and the light should extinguish. It’s a weird configuration how the sim works the active channel (personally I would prefer to have a hardware option that emulates the KMA-26 (and works with the logictech radio panels) and not have to rely on the ATC popup window to switch COM1 and COM2