By default, all sent files as in photos, videos, and audio messages are all downloaded automatically. Convenient, fast, but takes up a lot of memory in your phone.
If you have been using Telegram for a long time, check this out: Settings -> Data and Disk -> Disk Usage (wait for a couple of minutes before it processes all the cache memory) -> Clear the Cache. If you don't want to delete everything, you can delete the cache of each chat separately. Check how much storage is allocated for each segment, you will be very surprised.
When clearing your cache, you do not delete photos or audio recordings. They remain in the cloud and you still have access to them – you only need to download files over the Internet again.