Feature summary
When navigating directly to Special:Mute without specifying a username, i.e. https://en.wikipedia.org/wiki/Special:Mute presently you see only the "the username requested could not be found" error message.
It would be more useful if instead there was a standard input box to provide a username, ideally with autocomplete.

Use cases / benefits
This would allow muting (or unmuting) users without having to first navigate to their userpage or enter their username directly into the URI or search box.
I expect this would be particularly useful when (un)muting multiple editors. It's also worth noting that in my default window size (800px high, Firefox, Xubuntu linux) the mute link is not accessible without scrolling down in all skins (except in legacy vector where the line is half on and half not on the screen), increasing the desirability of navigating directly to the special page.

Background
As best I've been able to find, the current behaviour arose with the implementation of T331058 where it was listed as desired in the task summary, but it was not discussed in any of the comments there and there is no indication of any prior discussion or other origin.

The enhancement was requested at https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(proposals)#Add_a_username_box_to_Special:Mute by @Nyttend and @PrimeHunter