Many thanks for the replies!
For my data processing, I have to do the intersect based on the new Index2 and the inverse of Index1. Unfortunately, even if I generate my Index2 using the same approach, the below code gives me an error:
using InvertedIndices
intersect(Not(Index1), Index2)
Error message:
MethodError: no method matching length(::InvertedIndex{Vector{CartesianIndex{1}}})