So I consider taking a walk to clear your mind part of work for sure. I also consider reading HN or other engineering news/continued education sites to be part of work. And taking a coffee break to chat with co-workers about whatever (back when we worked in an office), including big-picture stuff and non-work related stuff, sure, that too.
That's all part of work when you do this kind of work. You can not just write code 8 hours a day, indeed, it's impossible, and if an employer tries to make you work that kind of sweat-shop environment (sometimes it seems like that's the actual goal of some Scrum implementations), it won't actually get them your best or even most productive work.
But there are people on HN who say that they literally spend the majority of their day the majority of days just doing things that are not work at all. I dunno, watching TV, running errands, riding their bike, mindlessly social media'ing, playing video games. Like they only spend a few hours a week on anything related to work at all.
I agree with GP that for me that's utterly soul-destroying, I end up feeling useless and unmoored. (The other day on the radio I heard someone reference a study that busy-ness to life satisfaction graphed as an upside down U, if you have too little free/leisure time you are unhappy, but people with too much are unhappy too, there's a sweet spot in the middle. Perhaps that's what we're talking about here).
But maybe different people are different.
Or maybe in new remote world, if you spend that time on projects you find rewarding (writing poetry, I dunno) instead of just goofing off, then it's not really "leisure" anymore, and you won't have that problem. If also you don't have any ethical problems with it (maybe your employer is awful and deserves to be drained of money), or just worry about getting caught.