Telegram will disclose users' phones and IP addresses to authorities at their requests, the messengers' founder and CEO Pavel Durov said on September 23.
If a friend was sending their pretty legally obtained books that they downloaded from different website via the TOR browser to themselves via Telegram to have an easy way to download them on their tablet, should they stop that and connect their tablet to their PC via an USB cable instead?
friend should nuke this crapware and use syncthing for such activities. if they happen to run jellyfin, they can use it to serve books as well, and by utilising the OPDS plugin it would allow compatible readers (e.g. Librera) to directly download books/comics to the device in a shop-like interface.