(i wouldn't count this as spoilers, it's the premise of the story and none of it is kept as a secret from the characters, but your definition of spoilers may vary)

Dungeon Crawler Carl is sci-fi, because the dungeon where all the fantasy-style magic takes place is like a huge Star Trek holodeck, with some privileged players having safety protocols turned on. Carl can't cast any magic when he's outside, like back on the surface. Changes to the player's body, like Carl's increased strength, seem to be real effects caused by real genetic and matter manipulation, but other people who've gone through body changes that only work in a fantasy setting start to worry that they now can never leave the dungeon, or they'll die if the computer running the dungeon environment crashes. Galactic politics between various alien species becomes more and more important to the story in later books.