If you need to keep a timer photo, your best course of action is to to send it again without the timer, explaining why you need to save it. Open communication is always superior to technical circumvention.
However, Telegram does provide a native, albeit limited, way to keep the photo temporarily . how to download timer photo in telegram
The second-device camera method works technically, but it produces low-quality results and breaches the trust that the timer photo feature was built upon. If you need to keep a timer photo,
Quickly tap the three-dot menu (Android) or the Share/Save icon (iOS). The second-device camera method works technically, but it
iOS is a "walled garden," making this process harder. The "Open With" feature is usually disabled for timer media. The operating system respects the app's request to not allow saving to the camera roll directly.