I’ve ridden too. I grew up in Maryland, we all rode back then. The horses still do the bulk of the work and they’re the ones to admire. The horses do get credit in Olympic events as I recall. I’m not disparaging equestrians, just pointing out how much of the physical activity is undertaken by the horse, something I’m sure you appreciate.
The obvious answer is basketball. I could ride the bench and wave a towel pretty effectively, and you could probably give me 5 minutes of playing time halfway though the third quarter without me meaningfully lowering the US team’s chance at winning. I’d never touch the ball on offense, obviously, and I’d be a hilarious defensive liability, but I know the game enough to stay out the way of the people who are good at it.
I think Racewalking, if I practiced. I’ve always wanted to do that.
Handball, maybe, for short spurts. I’d need to learn all the rules, though.
Frankly, I’m so awed by what darn near every Olympian can do that I doubt I could compete with any of them.
As with most sports, it’s a lot harder to do well than it looks. I really can’t figure it out, because they sure don’t look like they’re going that fast, but if you do the math, the world class guys are walking just a little less than ten miles an hour (a little over six minutes per mile), for over 12 miles (20km). A low percentage of people could run that fast for that long, let alone walk it.