Of the 2020 movies I've seen, the three best, in alphabetical order, were Da 5 Bloods, Judas and the Black Messiah, and Ma Rainey's Black Bottom. The latter two have 11 nominations between them. Da 5 Bloods has one, for Best Original Score. So there's one particularly large error, because Da 5 Bloods is better than at least 7 of the 8 movies nominated for Best Picture, and I saw them all.
Eight pictures get an honorable mention nod from me ... these are all very good movies (once again, alphabetical): Dick Johnson Is Dead (0 nominations), Minari (6), The Nest (0), Never Rarely Sometimes Always (0), Nomadland (6), One Night in Miami (3), She Dies Tomorrow (0), Totally Under Control (0), The Trial of the Chicago 7 (6). That adds up to zero nominations for five of my eleven favorite movies of 2020. If I have to narrow it down to one error, I'd go with Never Rarely Sometimes Always, which really deserves a lot of nominations.
As I said, I saw all of the Best Picture nominees, and they are all at the least good ... there are no stinkers. I was especially glad to see Promising Young Woman on the list.
Off the top of my head, here are my favorites among the actual nominees:
Best Picture: Judas and the Black Messiah
Best Actor: Chadwick Boseman
Best Actress: Carey Mulligan or Vanessa Kirby (I didn't see Andra Day)
Best Supporting Actor: Daniel Kaluuya
Best Supporting Actress: Maria Bakalova (I didn't see Glenn Close)
Best Director: Lee Isaac Chung for Minari
Best Adapted Screenplay: Kemp Powers for One Night in Miami (didn't see The White Tiger)
Best Original Screenplay: why not, Emerald Fennell for Promising Young Woman
Best Sound: Sound of Metal (only saw 3 of the 5)
Here is Sidney Flanigan in the ignored-by-Oscar Never Rarely Sometimes Always. This was Flanigan's first acting job in a feature film.