And how could this be done with buttons? Also, wouldn´t that be a bad
Sorry, i literally missed your reply up until now!
Hope you found a solution, if it was me i would have used a TextureButton node: they have all the nice things about buttons (pressed/toggle signal, mouse enter/exited signal) plus you can use your own texture on them.
Then, you can create 3 different control node , one for Item1, one for Item2 and one for Item3, (same position, one on top of the other) and put whatever you need inside of them.
When you click on the button (or hover the mouse) the respective ControlNode get showed and the others get hidden.
To make 3 buttons with the same dimension, alligned, you can either positionate them manually (it's not so hard since they are only 3) or make them child of the HSplitContainer node, in this way they get automatically positionated
Said that, there is probably a way to use the tab node, and include images into the label text, like https://godotengine.org/qa/72087/how-to-add-a-picture-to-the-text
(but i havent tested it personally)