https://t.me/tg_chat_webapp_protection_bot
(source: https://github.com/Pterko/tg-chat-webapp-protection-bot/commit/e54d35b809b1484fd34cf9600417eb756c57f0fb)

This MiniApp allows you to secure your Telegram chats using the WebApp (MiniApps) Telegram technology, powered by Recaptcha. Users will need to verify that they are not bots.

To utilize this bot as a user, you might want to consider using our hosted version of the bot: @tg_chat_webapp_protection_bot.

How to use it:
1. Add this bot to your chat.
2. Grant the bot administrator permissions.
3. Send the /enableProtection command from a user account to the chat to activate protection for this particular chat.
4. Optionally: Establish the rules for your chat using the /setRules command. Ensure that each rule begins on a new line.

Following these steps, all new users joining the chat will be required to complete a Recaptcha verification via the web app.

The bot doesn't give a link to the app itself. I suppose it would appear when the user joins the chat, but it would be better if you add information on how to use the bot.