the way: via iOS Shortcuts 😂

Screenshot of the whole step-by-step process the Resize for Telegram Stickers iOS Shortcut, which involves resizing the image to 512 pixels, then converting it to PNG before saving to your Photos app

If you want to make use of this and you're an iOS user yourself, maybe you'll benefit from this 😁 Get the shortcut here!

Note that you still have to send the image as a file when you send it in the Telegram chatbot 😆