Find the Contacts Section: Scroll down within "Privacy and Security" until you find the "Contacts" section.
Disable "Sync Contacts":
Find the option labeled "Sync Contacts" and toggle the switch OFF. It will typically turn gray or left-aligned to indicate it's disabled.
Delete Already Synced Contacts from Telegram's Cloud (Crucial for Full Opt-Out):
After disabling "Sync Contacts" (Step 5), you'll see telegram number database an option labeled "Delete Synced Contacts" in the same "Contacts" section.
Tap on "Delete Synced Contacts".
A confirmation prompt will appear, often stating that this will remove all previously synced contacts from Telegram's servers. Tap "Delete" or "Delete Synced" to confirm.
Note: It's important to disable "Sync Contacts" first, and then delete previously synced contacts. If you only delete without disabling sync, Telegram might just re-upload them later.
No New Automatic Additions: Telegram will no longer automatically upload new contacts from your device's address book to its cloud servers.
Your Existing Telegram Contacts Remain: Any contacts you've manually added to Telegram, or contacts you've chatted with previously, will still appear in your Telegram contact list and chats. Deleting synced contacts only removes those that Telegram identified and added from your phone's address book through the sync process.
Manual Contact Addition: You can still add new contacts to Telegram manually. You'll need their Telegram username or their phone number, and you can add them directly within the Telegram app.