Are you sure on that? I went onto the PC with the old Paint.net and compared. The edges of Super Sampling are definitely different from the edges of Bicubic. If you look at the attachment, the Super Sampling image is 264x264, whereas the Bicubic image is 262x262. Zooming in, the edges definitely look different.
Also, the result of Bicubic changed. On the old Paint.net, I don't get any artifacts around the edges. On the new Paint.net, I do get artifacts. Not nearly as much as Adaptive, but they're there. Lanczos also has heavy artifacting going on (it looks similar to Adaptive). Only Bilinear, Fant and Nearest Neighbor do not. Bilinear is the one that resembles the old Super Sampling results for edges the closest, but it doesn't come as close in quality.
It's a shame if Super Sampling goes the way of the Dodo. It had by far the best quality for the edges of transparent images. I tended to use AI upscaling tools to increase image sizes, but they were generally rather poor with the edges of transparent images, so I used Super Sampling for the Alpha.
Is there any chance another option will become available that focuses on the quality of the edges of transparent images, like Super Sampling did?
Here's a version with the 100% transparent areas converted to pink, so you can easily see the artifacts without first downloading and opening the image:
I should not be needing to remove semi-transparent parts of the image to deal with the artificing. Especially not when it used to be not needed at all.