This would honestly be a very boring category as the only thing that is different is you just walk which wouldn't make it fun to play nor watch.
also really hard to define, like you'd have to ban a whole ton of movement to make walking optimal
First off that sounds super boring, noone would run that except for people hungry for a free world record.
You said we're only allowed to walk. So no running or rolling, right? But you can triple jump vector to go a bit faster. You can long jump to move faster as well. You could cap dive, just dive, even just jumping would probably go a bit faster than walking. You'd have to make very strict guidelines to make this work, which would make it hell both to verify and to run. Just like almost every other "Any% but..." category on here you can submit to the main boards if you want to run it, it's just any%.