Pages that are using the old design:
System Settings > Connections > Proxy
System Settings > Connections > Cache
System Settings > Connections > Connection Preferences
System Settings > Connections > Windows Shares
System Settings > Applications > Launch Feedback
System Settings > Input devices > Mouse
System Settings > Display and Monitor > Display Configuration
System Settings > Display and Monitor > Compositor
System Settings > Display and Monitor > Night Color
System Settings > Power Management > Activity Power Settings
System Settings > User feedback
Settings > Users
Settings > Notifications (it's not fully aligned)
System Settings > Applications > Locations
System Settings > Default Applications
System Settings > Accessibility > [all of the subpages]
System Settings > Regional Formats > Formats
System Settings > Startup and Shutdown > Desktop session
System Settings > Workspace Behavior > General Behavior
System Settings > Workspace Behavior > Screen Edges
System Settings > Workspace Behavior > Touch Screen
System Settings > Workspace Behavior > Screen Locking
System Settings > Appearance > Fonts

I don't know if tabbed settings should be vertically aligned too, because this would create an inconsistency with other apps:

System Settings > KDE Wallet
System Settings > Date and Time
System Settings > Window Management > [all of the subpages]
System Settings > Task Switcher > [all of the subpages]
System Settings > Audio (I don't know if this one applies to this list, when there is just a few devices, there's a big blank space at the bottom. Also, there is headers with a semi-transparent black background, so it might look weird)
System Settings > Power Management > Advanced configuration (I don't know if another tab appears if something is triggered):