This works with GTK for me at least. I've been using Gnome+Wayland with 150% scaling for almost 4 years now, and I haven't noticed any issues with GTK. Actually, my experience is essentially backwards from yours—anything Electron/Chromium-based needed a bunch of command-line flags to work properly up until a few months ago, whereas GTK apps always just worked without any issues.

If you're using a high-DPI monitor, you might not notice the blurriness. I use a standard 110-DPI monitor (at 200% scaling in Gnome) and I notice it when the scaling factor is not an integer.

Or more precisely, I noticed it eventually as a result of my being primed to notice it after people on this site insisted that GTK cannot handle fractional scaling factors.

Compared to the contents of a browser's viewport, Emacs and the apps that come with Gnome are visually simple, so it took me a year or 2 to notice (even on a standard 110-DPI monitor used at 150% and 175% scaling) any blurriness in those apps since the app I'm most conditioned to notice blurriness is my browser, and Chrome's viewport is resolution independent except when rendering certain image formats -- text is always non-blurry.

Yes, Chrome's entire window can be quite blurry if Xwayland is involved, but it now talks to Wayland by default and for years before that could be configured to talk Wayland, so I don't consider that worth talking about. If Xwayland is not involved, the contents of Chrome's viewport is non-blurry at all scaling factors except for the PNGs, JPGs, etc. For a long time, when run at a fractional scaling factor under Gnome (and configured to talk Wayland) the only part of Hacker News that was blurry was the "Y" logo in the top left corner, then about 2 years ago, that logo's PNG file was replaced with an SVG file and the final bit of blurriness on HN went away.