what exactly is your problem
I would like to help, but I don’t know how
A great way to construct such interlocking parts is “The Boolean Tools Assistant.” I construct the slots by subtracting a rectangle (B) equal to the material depth times the insertion depth (A minus B) from the outer shape (A).
I also find “Resize Slots” very helpful for adapting the slots to the material thickness.
For example: Christmas Pyramid - Finished Creations - LightBurn Software Forum