This is about Inkscape 0.92 running on Ubuntu 18.02:

I am trying to find the easiest quickest way to just blur out part of a screenshot. I am hoping to apply some type of filter to some object, then move it into place, possibly adjusting its size etc so as to blur out the image or whatever that is underneath that object whose filter I have applied.

For this I believe it is the Gaussian Filter as indicated by viewtopic.php?t=15612#p58096

Specifically only (1) below (because I can't see how (2) applies to my goal of only blurring out part of an underlying screenshot):

v1nce wrote:draw a white opaque shape over the region you want to blur.
create a new filter
(1) add a gaussian blur primitive with backgroundImage (on the right) as a source
(2) add composite/in between (2) and sourceImage (on the right)

Apply filter onto the shape (=select your shape and check the newly created filter)

if you want a smoother transition :
(1) add a gaussian blur primitive with backgroundImage (on the right) as a source
(1') add a gaussian blur primitive with sourceImage (on the right) as a source
(2) add composite/in between (2) and (1')

First I insert my screenshot which is just a bitmap image.

Then I drew a rectangle with no fill and a red stroke. I believe the color doesn't matter because I just need something I can move and resize into place and so that it blurs out (censors) the underlying part of the image. The net result looks like this:



The only way to select that blurred rectangle object is to use the left mouse button and drag across an extent that I happen to know covers the rectangle. But that defeats the purpose of being able to move it by single mouse click and drag on the object after it the filter is applied, and I have to know where that rectangle happens to be. Why? Is this a defect or intentional?

The workaround, of course, is to draw all of my rectangles across the image, and then select each one of them and apply the Gaussian Filter to them. But I want to know why I couldn't do this in a more direct manner, so as to see the blurred text as I apply it, not in bulk after the fact.

Ok, granted, the workaround may in fact be easier in the long run since after the object is blurred, it might be difficult to do Node editing on the object because, well, it is blurred. Hence why I'm curious to know if this is intended behavior.

Update: If I do select the node tool, and move the node tool over the blurred rectangle very slowly, I can see intermittent red lines of the rectangle. Then I can select the line and then editing nodes show up. Then I can edit it. But still, I could not do normal selection. So this is yet another workaround I will use for now for this (possibly non-)defect.
Thanks!

The problem is nothing to do with the blurring, and everything to do with the lack of a fill. If you draw a rectangle with a stroke and no fill, without blurring it, you can only drag it around by the stroke, as mouse events "drop through" the empty fill. So the easiest solution to your problem is to give the rectangle a fill. As you note, by using Background Image as the source for the filter, it doesn't matter what colour the fill is - but the fact that it's actually present means that Inkscape will accept mouse events on it.