Er, yeah -- Murderbot 5 (and 6) will spoil you heavily for 4, and including several of the sort of plotty things that do lesson appreciation.

1-4 are a tightly knit plot arc. Once you've read those, 5 and 6 can be read in either order. (#6 was written after 5, but is set between 4 and 5, and is designed to not spoil 5 nor be spoiled by it. It's not exactly a side-quest but it's more character deepening than story advancing, if that makes sense.)