Install and launch the LastSeen -
Telegram Tracking app
on your phone to receive notifications when someone is online on Telegram. Tap on the active after entering your contact's Telegram number. That's it; you'll now be notified by Telegram whenever they go live.
On the Google Play Store and App Store, you may find a plethora of Telegram notification tracking apps. Depending on the app you downloaded, you may be prompted to provide your name and other personal verification information. Your Telegram contacts will appear on the app's screen as soon as you finish the authentication, and you will begin receiving notifications for every user that comes online and goes offline.