Not warzone maps, just maps in general. What free app or website would you say is best for creating or editing a detailed map?

Probably whatever is complicated, yet easy to use for you.

I have some suggestions:

https://www.redblobgames.com/maps/mapgen4/

https://www.redblobgames.com/maps/mapgen2/

https://azgaar.github.io/Fantasy-Map-Generator/

(azgaar maps could be saved in svg files and edited in inkskape)