In summary, you want QGIS to show you in its interface the bounding box coordinates of one or more selected geometries, without using Python.
Is this possible? Yes, with the magic of expressions, I show you.
@Gnafu I think, that for your case the ideal is to configure the
Map Tip of the layer.
The first thing is to clarify that the bbox is defined by four extreme coordinates, xmin,xmax,ymin,ymax. These coordinates define the minimum rectangle of a polygon or a group of geometries, and are the ones that we are going to show.
1.- Open the polygon layer properties dialog box. Then go to the display tab.
2.- click on the button with the eplison symbol (capital e, highlighted with a red box in the image), located at the top. Write the following expression
'Xmax y Xmin: '+to_string(round(x_max(collect($geometry, is_selected())),2)) + ',' + to_string(round(x_min(collect($geometry, is_selected())),2)) + '\n' +
'Ymax y Ymin: '+to_string(round(y_max(collect($geometry, is_selected())),2)) + ',' + to_string(round(y_min(collect($geometry, is_selected())),2))
Then, next - apply - Ok.
To test it, activate the Map Tip button
Now, select a polygon and place the cursor on it. You will see its extreme coordinates.
Then, add to the selection other polygons, you will see how the coordinates change