How can Parasite win Oscars in two FILM categories?

Because it was eligible in both categories. No controversy chez Cynthia. The only way to avoid this would be to introduce rule that it could only get nominated in 1 category and make a call at ballot counting stage which category that was - one it got most votes in/one it was highest placed in ranking/ maybe even give nominee the choice - and backfill from the number 6 choice in the category the double nominee film did not end up in.  Either that or ban foreign language films from being eligible for best picture - which of course is ridiculous as well as being xenophobic.