Don't plant anything along the walkway. It will make it look constricted.

You might get some ideas here.

https://www.gardenloversclub.com/garden-designs/walkway-garden/plants-for-walkways/

I would plant catmint or a low growing fountain grass, but that's just me...

I’d widen the path and but in a border. But that’s just me....

"I’d widen the path and but in a border. But that’s just me...."

Me, too. Walkways to front doors with nothing flanking them except lawn look sterile, cold, and uninviting to my eye. Even placing plants along a few strategic points along the path can make the whole thing look much more appealing if you don't want to or can't border the entire walkway.

Blue oat grass makes me sneeze when in flower. So flanking that walk with this plant might make it a gauntlet for anyone prone to hay fever. Otherwise based on your use of the descriptor "clean" and how minimalist the rest of the setting looks two long beds of herbaceous perennials with their inherent tendency to produce messy things like dead flower heads might not be right for you.