Best Sci-Fi/Fantasy books for my old boring dad?

Edit: Picked up "A Canticle for Leibowitz" for him - if you know a good book he might enjoy though, feel free to leave a comment as I'll either pass a list along to him, or use the list for future gifts to him. And thanks everyone for the great recommendations!

Looking for a short-ish, wide-appeal sci-fi or fantasy novel to gift to my dad for Christmas, in the Portuguese language - hopefully without strong religious components (more context and details below)

So my dad and I read a lot, but very different genres. I read almost exclusively sci-fi and fantasy, he likes biographies, historical, and religious books. Most out there book I know of him reading was The Walking Drum by Louis L'Amour which he LOVED and talks about regularly, yet I don't think he's read any other historical fiction.

He regularly asks about what I'm reading and always says he doesn't understand why I like sci-fi/fantasy. He's never tried them though. I'm fairly confident he would enjoy the genres, he does fine with their movies.

Anyway, for Christmas I want to get him a book in Portuguese. He went to Brazil for 2 years on a mission for his church and he's still fairly fluent. My hope is he'll enjoy getting exposure to the language, while also getting to try a sci-fi/fantasy book.

There are some difficulties in picking a book for him though...

1. He is pretty religious and probably can't handle anything with atheist topics, maybe best to avoid fantasy with strong religious components as well
2. It probably should be on the shorter side - I haven't read many standalone novels so I'm not sure what's popular. I'm worried he'll lose interest in an epic fantasy novel, for example
3. He loves humor - I'm not a huge fan so another reason I'm asking for help

We did read Bad Omens, he liked it a lot, wasn't one that I see myself re-reading - but I guess some religious topics are fine?

I once tried to get him to read Ready Player One, thinking that it had wide appeal and having loved the story myself... I forgot about Wade's atheist rant in the beginning though. My dad returned the book and kinda started a fight with me on how I must have some plan to de-convert him - and he assured me the book was propaganda for Satan... So yeah, definitely sensitive to religious topics.

An obvious choice, I think, is Hitchhiker's Guide To The Galaxy. I may go with this if nothing else comes up. I don't love the book (not my favorite flavor of humor) but I think he'd enjoy it - I'm just hoping for something that might get him hooked on the genres.

Another serious contender is The First 15 Lives Of Harry August. I really liked this one, but I worry the themes of death and mental health might not be great for him.

Thanks for any suggestions! I know this is a bit specific