“Science fiction” is kind of broad, most anime has elements of science fiction because the medium (i.e. not being real) lends itself to more fantastical ideas. I upvote others recommendations for steins gate and cowboy bebop, here are some offbeat recommendations.
If you like emotional anime, I really enjoyed Plastic Memories. The last couple of episodes especially really hit me, the running theme of the agency having non-human employees is kinda interesting.
Serial Experiments Lain is a psychological horror thriller type thing with very heavy sci fi elements. Considering it’s from the 90s, it’s commentary on the internet is surprisingly relevant these days. A bit artsy and kind of disappears up its own arse sometimes like Eva, but really interesting regardless.
Wonder Egg Priority is kind of sci-fi, tbh I don’t know where sci-fi ends and fantasy starts, but I really enjoyed it. Just forgive it for the fucking dire ending, I think they ran out of budget, which is a shame. Kind of a “monster of the week” setup with cool action. Killer soundtrack too.
Finally, Eden of the East is a series I’ll always recommend. A mystery/thriller series where a group of people have access to a concierge that can basically do anything and they have a vague mission to “change the world”. Borderline sci -fi because of the heavy use of technology as a plot device. Also has an underwhelming ending, but the rest is top tier.