Key points are BTRFS with Snapper, PipeWire, newer kernels and some other niceties from backports, proprietary drivers/codecs by default, VirtualBox support (which I’ve personally had huge problems with in the past on multiple distros). They also mention font tweaks, but I haven’t done side-by-side comparisons, so I’m not sure exactly what that means.
Edit: shoutout to Spiral Linux creator @sb56637 , who posted a few illuminating comments on this older thread: lemmy.ca/post/6855079 (if there’s a way to link to posts in an instance-agnostic way on Lemmy, please let me know!)