I'm a massive fan of walking for mental, psychological, and physical benefits and have been walking at least 25k steps a day for the last two years. The only (somewhat major) downside is that it takes quite a bit of time, some days, particularly weekends when I don't have work to do, I look at the clock and it's approaching dinner time and I feel like the day just disappeared without being able to sit down and relax at all.
25k is excessive in that regard and I wouldn't recommend that much, but 10k is incredibly achievable and I would highly recommend anyone make a habit of walking every day.
Wow, 25k is a LOT! I try to average 7-8k a day, and post-Covid I hope to bring that average to 10k a day. It's the perfect base to stay healthy for me, with all other more intense cardiovascular exercise (e.g. strength training or HIIT) being extra 2 or 3 times a week.
25k would really take a huge chunk out of my day, I think at least 3 - 3.5 hours or so. But it really depends, working from home means I'm sedentary all day. In other jobs you wouldn't have to squeeze everything into the few evening hours so much.
The biggest issue I have with walking is that the city becomes a bit boring. I love walking and exploring, but I've also lived in the capital city of my country for decades. Every day is new and brings new little experiences, yet also many similar ones. Especially because I'm always leaving and returning from and to the same place, there's a limit to my routes. I've walked the same streets thousands of times by now. On holidays in Europe or Asia I easily hit >40k steps daily because it's just so much fun, every corner brings something new, architecture, a river, a forest, a square or park, or lots of little shops or eateries or public art pieces.
Check out StreetComplete -- I find it a great way to give walks a little more purpose.