No, its sadly not an addon. It' all self code more ore less. For the Floor generation of the dungeon I took this Algorythm from Github Procedural-2D-Dungeon-Generator and Translated it to gdscript. And implemented a QuadTree to speed things up. Then after the Floor generation I wrote a algorythm to connect the endpoints of the floors to one Huge Graph.
For the Huge graph i wrote an algoythm that places the items down (Keys, Abilitys, Items, Upgrades and then Treasures). And Then I had to render the floor to the Tilemap.
There are a few plugins out there like ManiaMap so i took a bit inspiration from there Pipeline system.
If you want i can also dive a bit deeper in the Item Placing Algorythm.
I could also make my Github Repo public if that helps!
Thank you for playing!