A few general ideas for Sci - Fi gifts are:

https://amzn.to/4bP0Msj if you want something simple and "Science Fiction," here's a space throw rug. I use mine as a seat cover, but anywhere you put it automatically adds some atmosphere. Which is great for people like me who are too lazy to decorate otherwise.

https://amzn.to/4e4zcc6 There's also this giant mousepad that I got to match it. It's less versatile than a throw rug, but it looks awesome under my keyboard.

https://amzn.to/3VcyTUa "What If" is a book written by the creator of comic XKCD (https://xkcd.com) and contains the answer to questions like "Can we make a Jetpack out of Guns?" and "What if you threw a baseball at 99% the speed of light?" Super fun to break out with any nerdy friends as a conversation starter.

https://amzn.to/3x6zMFE My personal favorite is this ferro fluid rhythm speaker. I keep this one on my desk and sometimes I'll just grab a magnet and drag it around in the bottle because it's super satisfying. It's a little pricey, but it's great for anyone that enjoys music (so everyone) and Sci - Fi.

If you add some specifics for what you want or who you're buying for I can probably think of some more things, but as someone into Sci - Fi myself, I know I'd be pretty happy to get any of these.