I think there's a pressure to come up with good and thought provoking questions to end our posts with, but in many cases, I don't think this is necessary.

Don't set the bar high. Especially if you're doing something niche. If we want people to interact, give them something simple, since they may not know much about your topic. Many of my subs say they don't feel they have anything to add since they don't have the knowledge of the topic I do. Not that I'm an experts, I'm just a few months of personal research ahead of them.

I can tell them more in one post than they know about the whole topic and that can be intimidating. My regulars will interact with that stuff, and some new people may be impressed, but the simple ones where it's just a neat pic and I say "hey, what do you like about this?" or "you prefer the one on the right or left?" are typically more popular because anyone can say something, and that first comment is the critical one because it gets other people to comment as the ice has been broken.

Also, not sure if it helps, but I'll often add my question as a comment so it will look like someone already engaged while they're scrolling and hopefully be more inclined to click through and maybe comment.