To be rendered correctly, your tileset images have to have a rectangular bounding area for each tile. Then, within that bounding rectangle, you have your tile’s base. Your tileset is not set up correctly, there’s no way for Tiled (or even most game engines) to use it correctly. The tiles are arranged on an isometric grid, but they’re still drawn as rectangles, as that’s how 2D computer graphics typically work, and because that method allows for isometric tiles with height.
Here’s an example of a correctly set-up isometric tileset:
(Image source: https://opengameart.org/content/isometric-64x64-medieval-building-tileset)
Notice how the tiles are arranged in a way that you can split this image up into a grid of rectangles, each one containing one tile. In this specific case, the tiles have height, but that’s optional.