It's only available in public chat rooms private messages are not recoverable no matter the client.

I can run a reverse-engineered client that just logs all the messages I ever receive, if I don't care about TOS.

Chances are you won’t, though, because for virtually all chat rooms, why bother? And so in the vast majority of cases, Discord’s approach works well at achieving its outcome. Either no one will hoard data in violation of their legal contract with Discord, or any published/searchable logs will receive takedowns, and that’s just enough to have the intended effect.

In the context of FOSS project chat rooms that we’re discussing here, it is quite ironic that many FOSS community members will, predictably and with tacit or explicit support from their peers, openly break their legal contract with Discord in order to hoard chat logs for private or public use — while in the same breath demanding use of, and compliance with, legal contracts such as the GPL. Human beings certainly do excel at developing blind spots for cognitive dissonance when it’s to their benefit to do so.