When the Bucket Fill Tool is active you have to go all the way to the tileset at the bottom right to change the tile for filling.
It would be great if right-clicking a tile in the canvas would also change the active tile, the same way as when the Stamp brush i active.
Nice Idea. Although at the moment you could do the process a bit quicker with keyboard shortcuts: switch to brush (B), right-click on the tile you want, and back to bucket (F).
You’re not the first to request this, and I think it certainly makes sense to put the right-click capture behavior of the Stamp Brush also on the Bucket Fill Tool. It is covered by the following issue on GitHub: