I think it is quite well known that only Telegram Secret Chats are true E2EE. That said, Telegram is still not in the business of selling metadata actively like Whatsapp/Facebook/Meta are. As far as plain features go, Telegram is streets ahead of Whatsapp. But if I needed real “secret chat” I’d probably use Threema, SimpleX, Nostr, Jami, etc where I’m not tied to my mobile phone number or e-mail address.