Each Xitter page goes where X would put it. A new Appearance and decor section holds Theme, Profile decor and Avatar decoration. Passkeys sits under Security, Connected apps and API tokens under Apps and sessions, Move account, Import, Organisation and Automation under Your account, and Other instances, Note appeals and Staff notices under Privacy and safety. X's Display row opens Theme.
X's Settings list stays exactly as it is, plus one Xitter row near the top. It opens a grouped list (Appearance, Account, Security and apps, Federation, Staff and notes) with every Xitter page. That's the easiest place to add new pages later.
Same layout as A, but Theme and Profile decor open as a full-screen editor. A live preview of your timeline or profile sits beside the controls, with a Desktop/Phone switch, and nothing changes until you press Save. Every other page is a normal X pane.