Isekai Structures is gone as a separate module.
It used to own KTM2’s towns, dungeons, outposts and ruins. All of that content now lives inside Isekai Expansion itself.
That takes the Isekai Series from six modules to five: Core, Expansion, Tweaks, Cuisine, Melody.
What players need to do
Nothing. There is one fewer jar in the pack and not one piece of content less: structures generate as before, and loot chests, respawn altars and the rest of the structure-side features are all where they were.