The Guardian reports in its September 2022 article, “Step on it! Walking is good for health but walking faster is even better,” that "how fast you walk could be just as important for your health as how many steps you take." 

A study with 78,500 UK adults found that by walking 10,000 steps a day "you could lower your risk of dementia by about 50 percent, and for cardiovascular disease and cancer, you’d be lowering it between 30 to 40 percent. Walking faster is even better for all outcomes - dementia, heart disease, cancer and death."

They also point out that "The first 5,000 steps does much more good than the next 5,000 steps and so on" - and if the first unit gives you one unit of good, the next unit is another half unit of good."

After you've hit the 10,000 step mark you may get fitter and feel even better but it won't guarantee better outcomes. The sweet spot is 10,000 steps.