Does Safari on iOS need to support this feature? Because isn't the entire idea of smooth scrolling to implement the scrolling that was ALREADY natively implemented on iOS?
Basically, while Safari might not "support" this feature, they already force their version of smooth scrolling on every site inside their browser.
On Safari for iOS or MacOS, you already get smooth scrolling no matter what. So they might not support the spec, but you still get it no matter what.
The only explanation I have for IE/Edge is that it is IE/Edge, and no one really expects much from those browsers anymore regardless. If I had a nickle for everytime someone told me "IE doesnt support that", then I wouldn't need a day job.
Lastly, this isn't a critical site feature in most cases. If an IE user uses your site without smooth scrolling, will it really impact their experience in any way? Probably not. So this is an example when you can safely use this feature, the browsers that support it will offer nice smooth scrolling, and the ones that don't will offer the same experience that those browser users are already used to.
The smooth scrolling set by the "scroll-behavior" is not the same as the user initiated scrolling in iOS. It is scrolling behavior when triggered by a navigation API [0].
If you go to the website in OP and click the table of contents in Chrome and then Safari, you'll see the difference.
It's smooth scrolling when triggered by an action such as a fragment link or a JavaScript API, it's not referring to manual scrolling (eg scroll wheel, touch swipe).
Basically, while Safari might not "support" this feature, they already force their version of smooth scrolling on every site inside their browser.
On Safari for iOS or MacOS, you already get smooth scrolling no matter what. So they might not support the spec, but you still get it no matter what.
The only explanation I have for IE/Edge is that it is IE/Edge, and no one really expects much from those browsers anymore regardless. If I had a nickle for everytime someone told me "IE doesnt support that", then I wouldn't need a day job.
Lastly, this isn't a critical site feature in most cases. If an IE user uses your site without smooth scrolling, will it really impact their experience in any way? Probably not. So this is an example when you can safely use this feature, the browsers that support it will offer nice smooth scrolling, and the ones that don't will offer the same experience that those browser users are already used to.