[Turm]

Both Whatsapp and Signal store their messages in a sqlite-db as well! If your device is rooted/jailbroken, extracting the data is relatively simple (see e.g. here: https://towardsdatascience.com/analyzing-my-whatsapp-databas...)

[kuu]

You don't need to have it rooted, you can request the information: https://faq.whatsapp.com/526463418847093/