Telegram does have E2E encryption if you toggle secret chats, it's just not by default because most users don't care about privacy and just want the cool features.
In 5 years of using telegram, I'm yet to see a person who would initate a secret chat with me. Everyone who loves Telegram hypes how cool it syncs all their messages on all devices, including browsers, yet, being happy of using the most secure end-to-end encrypted messaging. Sad.
Stickers do work in Telegram secret chat, though. Only animated stickers don't, presumably in order to avoid leaking IPs. But a lot of cool features do work in secret chat.
