This is all using Manifold 8 terminology, which is hardwired in my brain and I'm not looking. Can translate if needed. (IMHO Manifold 9 terms are always more longwinded, but never more helpful than the terms used in 8.)
(1) If your individual areas have attributes (possibly shared by contiguous neighbours), first make points to record those attributes, using inner centroids.
(2) Union all areas (faster than dissolve).
(3) Decompose the combined areas (giving islands).
(4) Reapply attributes from the points in (1). You can make a helpful check for unexpected conflicts at this stage by counting distinct values.
If you want more detail, or more detailed steps, then post sample data, of course.