My usual go-to is to ask what their latest/current obsession is. It works really well for a few reasons:

• it's nice and simple to ask - it doesn't require a monologue/wall of text to set up, and it doesn't require you to know anything about them to ask it;
• it's both as personal and as low-stakes as they want it to be. They can give very intimate, in-depth answers if they feel like it, or they can just mention something like the latest film they enjoyed. There's no risk of making them uncomfortable by asking it;
• it lets you filter out boring people who don't really take interest in anything;
• assuming they do have interests, it often gives you plenty of opportunities to dive into deeper conversation;
• it's often engaging for them because they get to talk about something they're passionate about;
• it's often interesting for you because people talking about things they're passionate about is awesome (and often attractive).
• it's pretty much always relevant and fresh because their latest obsession will change over time. This makes it particularly great for things like dating sites/apps because people's bios will often be out of date and/or they'll have talked about the things mentioned in their bio so much that they're kind of sick of them.

I've actually had multiple people on dating sites tell me how great a question they think it is, and that they're going to use it themselves in the future. So obviously it's not just me who thinks it's a great question!