Are you a moderator or an admin? Does directly visiting /c/slug/1234/edit work?
Edit: No, it doesn’t. The category edit dialog is specified entirely by the slug.
@pmusaraj this route can’t work on sites that have fully-stripped-ascii or “none” slug generation; you need to include the ID UX: Move category editing/creation to its own page (#10973) · discourse/discourse@6f5d8ca · GitHub