I stopped using GIMP and started using https://www.photopea.com/. You get most Photoshop features for free (ad-supported) in a familiar interface and without having to install a large slow application.
Photopea is amazing.
Its 90% a clone of PS and is sooo much better than gimp.
I used it today to remove a white background on some of our icons to get a transparent png.
It was as easy as going i to the layer options, blend options, and drag the slider. It even has the option that you can hold alt and split the slider in 2 to get transparency blend as a gradient.
This would be a nightmare in gimp, and photopea does it non destructively.
And since its a web app you dont even have to install anything.
Amazing.
Nightmare is a bit hyperbolic I'd say. From memory, use the magic wand tool, select the white area. Selection menu, expand by 4 or 6 pixels. Colors menu, color to alpha, pick white. Done.