I have attempted an image blend, where I selected the Blend tool, and selected 'FG to transparent', and pulled the line horizontally across the image and it creates full white on the left and the white fades into the right side of the image. Which is a good start, however, I'd like to try something other than a white blend. How would I change from white? Thanks

Using a gradient FG to transparent, presumably you set FG to white to give a white-to-image blend. Single layer used, nothing else. Looks like (1) in the screenshot.

What is the purpose of the blend ? Usually it is one image into another or it might be a coloured or a patterned background.

Instead of applying the gradient to the image, add a layer mask Layer -> Mask -> Add Layer Mask The first option is white (full opacity) use that.

Make the layer mask active by clicking on the mask icon and paint in the canvas. The essentials, White is fully opaque, Black fully transparent, shades of gray something in-between. Apply a gradient to that. (2)

More examples see: https://www.gimp.org/tutorials/Layer_Masks/

Then you can put a layer under the image, whatever is transparent shows. (3) You can still adjust the layermask. You can move the layers around. It is a well used technique, keep practicing.

Well, I have this image that I'd wanted to lighten up, and tried a few things that didn't make it look better, so I thought lightening/brightening the right side possibly, where I can add some text, may lighten it up a bit as a whole, on the web page, but still not a great idea (yet), I'm open to more suggestions as to what could be done to it.

Any more clues as to what you want.

Do not try to to do everything on a single layer.

The image can be brightened in any number of ways. Color curves is the usual, but often duplicating the layer and putting the top in a "layer-mode" often works.

Do you really want a solid white block on the left embedded in your image? Is the web page white and that makes no difference. Make it transparent and that works with any background.

Back to using a layer mask. Of course, for transparency you need to export as a png or these days in webp format. Using jpeg? The transparency is flattened to white anyway. Up to you.

Thanks for your reply.

I'd like to see how it would look, where the blue from the image blends to the left into light blue, then light grey and then white. Can you describe how I might accomplish that, to see if what I envision will, actually look good?

Back to using a layer mask and a white-to-black gradient.

The image with the layer mask over a variety of backgrounds. Of course you can use a single background layer and just fill with a variety of colours to check the effect.

Toggle the background layer visibility on/off for comparisons.

see: screenshots

Thanks again for your reply
You had mentioned this "The image can be brightened in any number of ways. Color curves is the usual",
can you tell me about "color curves", I'm not familiar with that. Thanks

https://docs.gimp.org/2.10/en/gimp-tool-curves.html

Some alternatives, then it is up to you to experiment. You have plenty posts here, you have been using Gimp for some time.

Assuming you have decided on some sort of blend. Using a layermask work with the image active (or apply the blend later, up to you. Usually better to correct the photo first )

Check the attached screenshots.

(1) Colours -> Curves click-and-drag the curve to suit.

(2) Colours -> Brightness-Contrast. Adjust the sliders to suit

(3) For that particular photo Colors -> Auto -> White Balance gives a reasonable result.

(4) Colours -> Levels For a manual version of (3) Pick a white point and a black point.

Most devolve back to Curves. Levels has an 'Edit as curves' Brightness-Contrast has 'Edit as levels'