While officially isometric projection uses a 30-degree angle, because this way each axis has the same proportions, this does not work nicely with pixel art. As you can see from the brick tile in your image, the lines actually have a 2:1 ratio between x and y axis. The angle of these lines is actually atan(1/2)*(180/pi) ~= 26.565 degrees (see https://en.wikipedia.org/wiki/Isometric_video_game_graphics).
That said, you can use Tiled with your own tiles at 30-degree, if you adjust the tile size of the map (increasing the tile height until your tiles align perfectly). But you may want to consider using the 2:1 ratio in case you’re going for pixel art since it tends to look a lot cleaner.