New It movie did just come out so it's pretty fresh in the minds of a lot of people, plus some adults might already have had a Pennywise costume from when the first part came out two years ago (last year one of my neighbors was dressed as Pennywise). I expect most kids are either going to be in superhero costumes, Fortnite, or Minecraft.

It's only on rare occasions I see some more surprising costumes. A few years back I was pretty surprised when one little girl I saw was dressed as a Little Sister from Bioshock (and when I told her "oh wow a Little Sister, awesome" she turned to her mom and said "see I told you someone would recognize what I am!"), one year some teenagers came dressed up as characters from Valve games like Left 4 Dead 2 and TF2 (I recall one guy was a Scout and one girl was dressed like Ellis), and last year one teenage girl was dressed as Frisk from Undertale (and by an amazing coincidence I was playing Deltarune when she came to my door so I actually asked her "hey did you check out the new game, Deltarune, yet?" and she was was surprised by me mentioning a new Undertale related game had just come out, I bet she immediately got on her computer after she got home just to make sure I wasn't bullshitting).