There are some third party clients you can used to receive and send message on Apple Watch.
TGWatch for Telegram: https://apps.apple.com/app/id6469582116
Pros
Free to receive / send telegram messages
Support text / photo / audio / sticker / gif message on Apple Watch
Cons
Don't support video and location messages on Apple Watch
Pigeon for Telegram: https://apps.apple.com/app/id1671939892
Pros
It's a standalone watch app, which can run without companion app.
Support more message types than TGWatch, like video / contact / location message.
Cons
Need paid even only want to send message, the price is high.
In the Telegram iOS Talk Channel there was a announcement on 15th September that a new Telegram Watch App is in development.
https://t.me/TelegramiOStalk/141096