If you have updated your Telegram app, you can now do a spoiler text formatting.
Select any part of your message when typing and choose ‘Spoiler’ in the formatting menu to hide the text under an animation in chat, as well as in the chat list and notifications.
You can tap the animation to reveal the hidden text. Spoilers can also be combined with other text formatting, including links.
On MIUI devices, tap the three dots ⋮ in the top-right corner to show the formatting options.
If you want to see how it is done in a video, watch it in action below: