Godot Version
4.3
Question
Hey when I use the standard 2d character with script and a collision body it falls trough the ground
but when i add a collision to the tile inside its physics layer 0 the character just stucks and is not able to move.
Isometric tilesets do not actually introduce a third axis but just create an illusion of the axis existing at the expense of the y axis that would normally be used for things like jumping in a 2d platformer game.
This means that your code that basically moves the character along the y axis until it hits “the floor” (a collider) will not work since the y axis is now both up/down and back/forward (if you move your player “down” you are also moving it forward).
And again since your tileset is now representing another axis, if you put a collider in your floor it will not allow your player to exist there (try to transform it in your head in a platformer game and think of it as a giant platform basically filling the entire screen, this is what is happening here, you still only have 2 axes)
If you want to have jumping in a game like this you need to virtually track a fake third axis in your code and then change position of your player based on that (while in reality just moving it along the y axis up and down), together with a shadow this would create an illusion of jumping.