This build has two big things going for it: 1) fixes to the Save Configuration dialog (sorta), and 2) some absolutely massive performance fixes to the main rendering engine when working with very large images.
Save Configuration dialog: Some folks have reported that they can't get the Preview to work, even though saving and loading works fine. I don't have a fix for this yet (AFAIK), but at least you'll be able to see what the actual error is now so that you can send it to me. It will show up in the standard error dialog along with the almost useless "Preview: (error)" text that displays at the top.
Rendering engine: Before this update, Paint.NET has been very bad about handling very large images. I'm talking images that are on the order of 32,000 pixels large on either dimension (width or height). Zooming and panning often result in very long delays where the app just hangs until it figures itself out -- and we're talking 30, maybe even 60, seconds, even with a $1000 CPU like an overclocked Intel Core i9-7900X. I spent the last week optimizing this and replacing the data structures and work queue management code, and now this should all be working good. It's not 60 FPS, so there's still some work left when the time comes for it, but it's very usable now! The worst delays might be on the order of 100-200ms, so they just feel like kind of a choppy framerate sometimes.
Download link: https://www.getpaint.net/files/zip/test/paint.net.4.107.7077.41990.install.zip
(I'm adding this to the auto-updater right now)
Changes since the previous alpha (build 7070):
Fixed: Optimized rendering engine to remove huge lag spikes (30+ seconds) when zooming or panning very large images (e.g. 32K x 32K pixels).
Improved: Added error reporting to the Save Configuration dialog. Instead of just saying "Preview: (error)", you'll also get the standard error dialog that includes the exception which can used for troubleshooting.