Complete documentation of the iOS Settings app's URL scheme
As of iOS 13.1, these URLs are back, and have been exhaustively documented on the MacStories website by Federico Viticci. Please note that the linked page is being actively updated, and contains other useful background and tips such as how to link to the settings for third party apps, so probably a good idea to follow the linke through to that site for the full info:

Settings URLs
iCloud

iCloud: prefs:root=CASTLE
iCloud Backup: prefs:root=CASTLE&amp;path=BACKUP


Wireless Radios

Wi-Fi: prefs:root=WIFI
Bluetooth: prefs:root=Bluetooth
Cellular: prefs:root=MOBILE_DATA_SETTINGS_ID


Personal Hotspot

Personal Hotspot: prefs:root=INTERNET_TETHERING
Personal Hotspot ⇾ Family Sharing: prefs:root=INTERNET_TETHERING&amp;path=Family%20Sharing
Personal Hotspot ⇾ Wi-Fi Password: prefs:root=INTERNET_TETHERING&amp;path=Wi-Fi%20Password


VPN

VPN: prefs:root=General&amp;path=VPN


Notifications

Notifications: prefs:root=NOTIFICATIONS_ID
Notifications ⇾ Siri Suggestions: prefs:root=NOTIFICATIONS_ID&amp;path=Siri%20Suggestions


Sounds

Sounds: prefs:root=Sounds
Ringtone: prefs:root=Sounds&amp;path=Ringtone


Do Not Disturb

Do Not Disturb: prefs:root=DO_NOT_DISTURB
Do Not Disturb ⇾ Allow Calls From: prefs:root=DO_NOT_DISTURB&amp;path=Allow%20Calls%20From


Screen Time

Screen Time: prefs:root=SCREEN_TIME
Screen Time ⇾ Downtime: prefs:root=SCREEN_TIME&amp;path=DOWNTIME
Screen Time ⇾ App Limits: prefs:root=SCREEN_TIME&amp;path=APP_LIMITS
Screen Time ⇾ Always Allowed: prefs:root=SCREEN_TIME&amp;path=ALWAYS_ALLOWED


General

General: prefs:root=General
General ⇾ About: prefs:root=General&amp;path=About
General ⇾ Software Update: prefs:root=General&amp;path=SOFTWARE_UPDATE_LINK
General ⇾ CarPlay: prefs:root=General&amp;path=CARPLAY
General ⇾ Background App Refresh: prefs:root=General&amp;path=AUTO_CONTENT_DOWNLOAD
General ⇾ Multitasking (iPad-only): prefs:root=General&amp;path=MULTITASKING
General ⇾ Date &amp; Time: prefs:root=General&amp;path=DATE_AND_TIME
General ⇾ Keyboard: prefs:root=General&amp;path=Keyboard
General ⇾ Keyboard ⇾ Keyboards: prefs:root=General&amp;path=Keyboard/KEYBOARDS
General ⇾ Language &amp; Region: prefs:root=General&amp;path=INTERNATIONAL
General ⇾ Dictionary: prefs:root=General&amp;path=DICTIONARY
General ⇾ Profiles: prefs:root=General&amp;path=ManagedConfigurationList
General ⇾ Reset: prefs:root=General&amp;path=Reset


Control Center

Control Center: prefs:root=ControlCenter
Control Center ⇾ Customize Controls: prefs:root=ControlCenter&amp;path=CUSTOMIZE_CONTROLS


Display

Display: prefs:root=DISPLAY
Display ⇾ Auto Lock: prefs:root=DISPLAY&amp;path=AUTOLOCK
Display ⇾ Text Size: prefs:root=DISPLAY&amp;path=TEXT_SIZE


Accessibility

Accessibility: prefs:root=ACCESSIBILITY


Wallpaper

Wallpaper: prefs:root=Wallpaper


Siri

Siri: prefs:root=SIRI


Apple Pencil

Apple Pencil (iPad-only): prefs:root=Pencil


Face ID

Face ID: prefs:root=PASSCODE


Emergency SOS

Emergency SOS: prefs:root=EMERGENCY_SOS


Battery

Battery: prefs:root=BATTERY_USAGE
Battery ⇾ Battery Health (iPhone-only): prefs:root=BATTERY_USAGE&amp;path=BATTERY_HEALTH


Privacy

Privacy: prefs:root=Privacy
Privacy ⇾ Location Services: prefs:root=Privacy&amp;path=LOCATION
Privacy ⇾ Contacts: prefs:root=Privacy&amp;path=CONTACTS
Privacy ⇾ Calendars: prefs:root=Privacy&amp;path=CALENDARS
Privacy ⇾ Reminders: prefs:root=Privacy&amp;path=REMINDERS
Privacy ⇾ Photos: prefs:root=Privacy&amp;path=PHOTOS
Privacy ⇾ Microphone: prefs:root=Privacy&amp;path=MICROPHONE
Privacy ⇾ Speech Recognition: prefs:root=Privacy&amp;path=SPEECH_RECOGNITION
Privacy ⇾ Camera: prefs:root=Privacy&amp;path=CAMERA
Privacy ⇾ Motion: prefs:root=Privacy&amp;path=MOTION\


App Store

App Store: prefs:root=STORE
App Store ⇾ App Downloads: prefs:root=STORE&amp;path=App%20Downloads
App Store ⇾ Video Autoplay: prefs:root=STORE&amp;path=Video%20Autoplay


Wallet

Wallet: prefs:root=PASSBOOK


Passwords &amp; Accounts

Passwords &amp; Accounts: prefs:root=ACCOUNTS_AND_PASSWORDS
Passwords &amp; Accounts ⇾ Fetch New Data: prefs:root=ACCOUNTS_AND_PASSWORDS&amp;path=FETCH_NEW_DATA
Passwords &amp; Accounts ⇾ Add Account: prefs:root=ACCOUNTS_AND_PASSWORDS&amp;path=ADD_ACCOUNT


Mail

Mail: prefs:root=MAIL
Mail ⇾ Preview: prefs:root=MAIL&amp;path=Preview
Mail ⇾ Swipe Options: prefs:root=MAIL&amp;path=Swipe%20Options
Mail ⇾ Notifications: prefs:root=MAIL&amp;path=NOTIFICATIONS
Mail ⇾ Blocked: prefs:root=MAIL&amp;path=Blocked
Mail ⇾ Muted Thread Action: prefs:root=MAIL&amp;path=Muted%20Thread%20Action
Mail ⇾ Blocked Sender Options: prefs:root=MAIL&amp;path=Blocked%20Sender%20Options
Mail ⇾ Mark Addresses: prefs:root=MAIL&amp;path=Mark%20Addresses
Mail ⇾ Increase Quote Level: prefs:root=MAIL&amp;path=Increase%20Quote%20Level
Mail ⇾ Include Attachments with Replies: prefs:root=MAIL&amp;path=Include%20Attachments%20with%20Replies
Mail ⇾ Signature: prefs:root=MAIL&amp;path=Signature
Mail ⇾ Default Account: prefs:root=MAIL&amp;path=Default%20Account


Contacts

Contacts: prefs:root=CONTACTS


Calendar

Calendar: prefs:root=CALENDAR
Calendar ⇾ Alternate Calendars: prefs:root=CALENDAR&amp;path=Alternate%20Calendars
Calendar ⇾ Sync: prefs:root=CALENDAR&amp;path=Sync
Calendar ⇾ Default Alert Times: prefs:root=CALENDAR&amp;path=Default%20Alert%20Times
Calendar ⇾ Default Calendar: prefs:root=CALENDAR&amp;path=Default%20Calendar


Notes

Notes: prefs:root=NOTES
Notes ⇾ Default Account: prefs:root=NOTES&amp;path=Default%20Account
Notes ⇾ Password: prefs:root=NOTES&amp;path=Password
Notes ⇾ Sort Notes By: prefs:root=NOTES&amp;path=Sort%20Notes%20By
Notes ⇾ New Notes Start With: prefs:root=NOTES&amp;path=New%20Notes%20Start%20With
Notes ⇾ Sort Checked Items: prefs:root=NOTES&amp;path=Sort%20Checked%20Items
Notes ⇾ Lines &amp; Grids: prefs:root=NOTES&amp;path=Lines%20%26%20Grids
Notes ⇾ Access Notes from Lock Screen: prefs:root=NOTES&amp;path=Access%20Notes%20from%20Lock%20Screen


Reminders

Reminders: prefs:root=REMINDERS
Reminders ⇾ Default List: prefs:root=REMINDERS&amp;path=DEFAULT_LIST


Voice Memos

Voice Memos: prefs:root=VOICE_MEMOS


Phone

Phone: prefs:root=Phone


Messages

Messages: prefs:root=MESSAGES


FaceTime

FaceTime: prefs:root=FACETIME


Maps

Maps: prefs:root=MAPS
Maps ⇾ Driving &amp; Navigation: prefs:root=MAPS&amp;path=Driving%20%26%20Navigation
Maps ⇾ Transit: prefs:root=MAPS&amp;path=Transit


Compass

Compass: prefs:root=COMPASS


Measure

Measure: prefs:root=MEASURE


Safari

Safari: prefs:root=SAFARI
Safari ⇾ Content Blockers: prefs:root=SAFARI&amp;path=Content%20Blockers
Safari ⇾ Downloads: prefs:root=SAFARI&amp;path=DOWNLOADS
Safari ⇾ Close Tabs: prefs:root=SAFARI&amp;path=Close%20Tabs
Safari ⇾ Page Zoom: prefs:root=SAFARI&amp;path=Page%20Zoom
Safari ⇾ Request Desktop Website: prefs:root=SAFARI&amp;path=Request%20Desktop%20Website
Safari ⇾ Reader: prefs:root=SAFARI&amp;path=Reader
Safari ⇾ Camera: prefs:root=SAFARI&amp;path=Camera
Safari ⇾ Microphone: prefs:root=SAFARI&amp;path=Microphone
Safari ⇾ Location: prefs:root=SAFARI&amp;path=Location


News

News: prefs:root=NEWS


Health

Health: prefs:root=HEALTH


Shortcuts

Shortcuts: prefs:root=SHORTCUTS


Music

Music: prefs:root=MUSIC
Music ⇾ Cellular Data: prefs:root=MUSIC&amp;path=com.apple.Music:CellularData
Music ⇾ Optimize Storage: prefs:root=MUSIC&amp;path=com.apple.Music:OptimizeStorage
Music ⇾ EQ: prefs:root=MUSIC&amp;path=com.apple.Music:EQ
Music ⇾ Volume Limit: prefs:root=MUSIC&amp;path=com.apple.Music:VolumeLimit


Photos

Photos: prefs:root=Photos


Camera

Camera: prefs:root=CAMERA
Camera ⇾ Record Video: prefs:root=CAMERA&amp;path=Record%20Video
Camera ⇾ Record Slo-mo: prefs:root=CAMERA&amp;path=Record%20Slo-mo


Books

Books: prefs:root=IBOOKS


Game Center

Game Center: prefs:root=GAMECENTER