Sure.
Telegram uses encryption that allows themselves to read your messages. This shortcut allows them to restore messages, outside of secret chats, when you install the app on a new device. It also makes distribution of your messages to large groups much easier for themselves.
Another shortcut Telegram took was to hide your phone number only when it wasn’t in the contacts already. There are a limited number of possible phone numbers, so discovering a “hidden” one is possible.
Another shortcut Telegram took has to do with the default settings they chose.
Rather than defaulting to using secret chats, they chose to default to not secret chats for every new discussion and group. This isn’t in the users’ best interests, so Signal encrypted everything and doesn’t offer non-secret chatting.
Regarding SMS, Signal had made this mistake for a while too, because they chose to drop encrypted SMS, then dropped SMS entirely later. Signal let perfect be the enemy of good.