I’ve participated in competition and have won awards for my writing in university, and we’re always encouraged to submit our piece to a journal or magazine after the fact if the school hadn’t published us first.
There are tons and tons and TONS of journals and periodicals that exist for you to publish in, but you’re probably going to have to apply to like 50 until one accepts you. Still, most of these are for things more fancy, either very serious realistic fiction or creative non fiction. I’ve never seen anything sci-fi or fantasy published by these journals (although I didn’t write in those genres so maybe I’m biased)
Sci-fi periodicals do still exist, but are filled to the brim with woke slop and stories that just recount someone’s EVE Online shipping run or DND session.
We will never get sci-fi equal to Foundation or Neuromancer serialized on release again