When I connect this keyboard to Garageband on my Macbook Pro (running Big Sur), the keyboard is detected, everything seems to work, but the sustain pedal doesn't seem to work correctly. When I press the sustain pedal it creates a tone which continues until I power down or disconnect the keyboard. The keyboard has old-style round MIDI connectors, and I connect to the Macbook via USB. Other than the sustain everything else seems to work properly, keys play, velocity seems accurate, etc; it's just the sustain that doesn't seem to work. Any suggestions?

Thanks for the very detailed response. I tried all your suggestions. When I created a short track, each time I pressed the sustain pedal it shows a note (E3) playing on both the press and release. The orange line is at zero and then jumps to a higher position partway through, where it stays. I can't see how to attach a screenshot here or I would attach it.