If you found this in your device's "Telegram Documents" or "Telegram Video" folder, it is likely a video that was downloaded but not explicitly "saved to gallery/downloads" with its original name.
Since the filename is randomized, you cannot determine the content by the name alone. To see what is in the file, you can: AgADtAIAAkXhEEQ.mkv
The .mkv extension indicates it is a Matroska Video file, which is a high-definition container format capable of holding multiple audio tracks, subtitles, and high-quality video. How to Identify the Actual Content If you found this in your device's "Telegram