@Testarossa44 I really, really feel for you about losing your dad's messages.
Not quite the same thing but I used to email my mum everyday (from my work account. Which is allowed). My company had a cyber attack in June and thus far they've only managed to restore our emails for 1 year so back to June 2020. My mum died in September 2020. I've lost years and years worth of our emails.
I could (and will eventually) ask for them the be restored but understandably, as they are private, they'll be lowest priority.
My mum never had WhatsApp. I wish she had upgraded to a smart phone. W.A would have been a gamechanger for her (she had terrible mental health and was virtually agrophobic when we lost her)
Things like this add to the misery of the actual loss.