I have a non-shipping internal test app which is macOS only. It uses AppKit and .xib files to describe the UI.
On Sonoma, the app renders with most of its UI quite blurry, as if a 10 pixel Gaussian blur were applied to it. The blur is applied to entire views, not just the text. It doesn't vary with screen resolution. I observed this behavior with one of the Sonoma betas but I think it went away when I re-launched the app - at any rate, I forgot about it.
I've updated my dev machine to the shipping Sonoma and the problem is extant. I opened up the .xib file in Xcode and the blurriness is visible there too. I haven't applied any effect layers to my UI.
Not all of the views in my UI are blurry.
Has anyone else seen this?