I’m using the most recent version of Tiled, yet I cannot place down any tiles using any of the tools.
The tileset is an isometric one that was imported using a single image, and in the “Tileset” window it is showing that the tiles exist. I have even made sure to select that tiles when I try to use the tools on this isometric map.
It looks like you’ve accidentally enabled the “Terrain” painting mode, but since you’ve got no Terrains set up, this won’t do anything. To be able to place tiles, disable the Terrain mode, which is the map icon next to the two dice.
I guess it would be a good idea to disable this button when no Terrain Set has been selected.
