Only if they have direct access to a phone that is unlocked and has the unlocked app installed.
Telegram encrypts all messages and refuses to provide user data when asked. To view someone's messages, you must first access the app on their phone.
Because they lack the encryption keys to Telegram, law enforcement authorities are unable to make sense of the Telegram data they receive from ISPs. The use of bots guarantees that the user's identity remains hidden, making it impossible to track down those who promote illegal content and terrorism.