AI slop at work is an absolute waste of time and effort.
But your dad is trying to write his story, probably because he wants to leave something behind so he’s not forgotten. It might be cliche-riddled but AI is helping him write his experiences in a form he’s happy with and it’s still his story even if he got help.
He’s also probably only writing it for an audience of one - you. So don’t shit on it, read it. Or you might regret it.
If the father is really into the tech side of it (as opposed to pure laziness), I'd ask him for the prompts alongside the generated text and just ignore the output. The prompts are the writing that is meant for the original commentor, and it is well worth it to take the tact of not judging those by their writing quality independently.
If you're writing something for an audience of one, literally nothing matters more than the connection between you and the reader. As someone with a father who's getting on in years, even imagining this scenario is pretty depressing.
However, I can assure you if his audience is one person, he is that person. He is not writing for me.