Their e2e encryption only applies to 1-to-1 communication in the form of Secret Chats, which can be opened from a menu multiple clicks away. Default chats and group chats are not e2e encrypted and contents are fully visible to Telegram. This however enables lot of the features Telegram has that Whatsapp/Signal do not (seamless use with multiple clients, powerful search, history is retained after switching phones etc..)

- Weird hand-rolled crypto protocol of questionable quality (MTProto). Probably fine in practice, but leaves a bad taste in your mouth, and their marketing to prove it made it worse. It has been through a few revisions since initial scrutiny.

- Only Secret Chats are E2EE. Normal use is just subject to transport encryption. However, this is true for any platform with server-side chat history.

"leaves a bad taste in your mouth" - May be you should not try to eat a protocol ?

I'm unsure if you're unfamiliar with this phrasing or are simply trolling.

If the latter, well played.

It is not default option there. End users need to always remember that they need to use „Secret chats“

They lied. Or are technically incompetent. Or both.