Mine was like that, too. Sometimes even if I tried open-ended questions, he just gave short answers. And once he got older, I tried a lot to extend conversations because I never knew which might be the last. But most of my favourite memories with him are just doing things together - gardening, woodworking, once we drove out somewhere and just enjoyed to view in silence. Having something to do with your hands can sometimes make conversation easier. Asking to see his photo books is a good one, too, because he can tell you the background of the photos.

If you need ideas, just googling "questions to ask your parents" will get you a good list of potential convo starters and of course taking an interest in his work, hobbies, other things he likes helps. Don't be too hard on yourself if he just isn't the chatty type, though.

Ask him what his favorite things are (pick one topic - hobby, place, car, whatever he seems like he kind of likes) and ask him to tell you about it/why he likes it. People generally love to talk about things they love. Hopefully you like it/understand the interest. And actually listen and stay engaged. Ask questions about things he's vague on.

Conversations are two way streets. Hopefully you also find an intersection of interests yoy both like and then you can both dive into

Any common hobbies? You can talk about it.

Or a tv show/movie you both like. Sometimes I'd recommend a movie to my dad and we would watch it at the same time. We don't talk much during the movie but have a few chat while watching. We even do this while watching the news sometimes.