How to create loop cut through an object? To make things easier to understand, I have some photos below.

Now, if I create a 4x4 tile, then extrude the outer 12 squares, I get a cup-shaped object.



But if I create a Loop Cut on this object, you can see that it doesn't reach to the inside of the object.



How do I make it so that a loop cut reaches through the entire object?

Thanks for taking the time to read my post!
Loop cut is always made on one loop of faces.
In your example you have 2 separate loops so it cannot be cut at once with this tool.

What you can do is to make one loopcut for each face loop (inner &amp; outer):


or use Knife tool K with Z (cut through) option enabled (the Z key is not captured in the example). Hold Ctrl to make a cuts in the middle of edges or if you want to place it some were else but have it accurate press C to constrain the direction of the cut to 45 degree steps.