Nicola points to a 2015 study of 300-plus female twins that revealed a fascinating link: Having more powerful legs—a metric captured by sitting in a machine and pushing one foot as hard and fast as possible against a pedal—is associated with relatively better cognition 10 years later, measured by performance on tests of memory and processing speed.
The article goes on to suggest gym-equipment training exercises, but regularly pushing a heavily loaded pedal via cargo-cycling seems like a much more obvious solution that doesn’t require a gym membership.
I think you’re categorizing cycling as cardio because that’s what happens on a stationary bike at the gym. When you’re riding a bike in the wild, you frequently come to a complete stop and then have to bring it up to speed again. Even at a high gearing ratio, this is not a slow-twitch muscle activity. With increased load like additional cargo, the resistance is even more significant.