Iso game background tile sprite help

Hi, I am new to Gdevelop and I am having difficulty with making the isometric games.
I am wondering if anyone could tell me how I can make the background tile sprites have boundaries.
The example game that loads up has boundaries where the character cant walk, how would i re-create such boundaries with my own background tiles?

You need to edit the “hitbox” for each background sprite, so that it only covers the parts of the graphic that you don’t want the player to walk on. This is how the example isometric game works, although it isn’t obvious that’s how it is doing it.

In GD5 you can access the hitboxes, by double-clicking on the object in the list of objects, then on “EDIT HITBOXES”, then on “USE A CUSTOM COLLISION MASK”, then on the + icon. This will create a four-sided hitbox whose points you can drag around to position the barrier where you want it to be. If you need more than four points to make the right shape, click the + icon within the circle.

There is a restriction that all hitboxes must be convex, so you couldn’t do (for example) an H-shaped hitbox. What you would need to do for that is create three hitboxes (two vertical rectangles and one horizontal) by clicking the + icon three times and arrange them to make the H shape. It doesn’t matter if the hitboxes overlap, any collision with any hitbox will be counted as a collision by the GDevelop engine.

why did I not figure that out!? thank you so much for your help its so obvious now I know but I couldnt find any more help/ info about it anywhere. Thanks!!