For the group item to activate, more than one item must be selected.

Sorry, I had never tried this. Skip the grouping and aligning. I have tried the following.

Set the wrapping for your picture to be behind text.
Set the wrapping on the textbox to be in front of text. Set the fill for the textbox to no fill.

Move the two to be in the same position and have the same size. Once you have done this, you will be able to get to the picture only by moving the textbox so you can click on the picture.

Ordinary text, not in the textbox, can be between the two layers. You will probably want to avoid this.

Make sure that the color of the text in the textbox will contrast with your picture.

When you said textbox, I assumed that you meant a classic textbox, not some sort of text form field for people to type in. (Such a field could be inside a textbox.) That right-clicking on a textbox gives you a disabled group command tells me that we are talking about the same kind of textbox.