I cannot select any object after it was Send-to-Back.
That's a catch-22. You have to move the object(s) in front of it before you can select it. Just remember their position by looking at the X and Y values in the inspector. This way you can make sure you place them back exactly where they were after.
I don't have any objects in front and I cannot select this one which was moved back by Send to Back.
A text layout is also an object. You'd have to reduce its size so you can get to your object to select it.
I have experimented with a blank page and placed several different shapes on it. I moved one shape to the back using Send to Back and deselected it.
After deselection of the shape Send to Back this shape is not selectable again. There is no way to selected it and move it. The only remedy is to delete the page.
When using send to back, the object is placed as the first "layer" (similar to a photoshop layer) below the main text layout boundary. All you need to do is re-size that layout boundary until the image is revealed and then you can select it.
Selecting shape after it was Send-to-Back
