I'm a bit fuzzy on the details, but late July/early August 2023 there were rumors in certain circles regarding a potential Telegram session takeover exploit or some other scary weirdness. It ended up being a keyword (or probably URL) that was on Telegram's blocklist. Sending it to someone in a private chat resulted in account restrictions or session terminations, iirc.
Seems like instead of having a functioning moderation team, Telegram uses extremely lazy automation and hopes nobody will care.