Devs and Maniac are the first things that come to mind. I've seen those already recommended, so I'll add Fringe to the list. It is a bit more like X-Files in structure. There are lots of "monster of the week" style stories that tie into a larger overarching narrative. It handles its lore a lot better than X-Files did and wraps up rather nicely in my opinion. I'm not sure if it is still the case but it used to be streaming for free on IMDB.

Another good X-Files adjacent show is Evil, although I wouldn't really classify it as scifi. Take X-Files and swap out the aliens and the FBI for demons and the catholic church.