GNOME 3 had a hardware accelerated compositor on release in 2011.

Ubuntu came with Compiz by default in 2007: https://arstechnica.com/information-technology/2007/11/ubunt...

“Ubuntu 7.10 is the first version of Ubuntu that ships with Compiz Fusion enabled by default on supported hardware. Compiz Fusion, which combines Compiz with certain components developed by the Beryl community, is a compositing window manager that adds a wide range of visual effects to Ubuntu's desktop environment. The default settings for Compiz enable basic effects—like window shadows and fading menus—that are subtle and unobtrusive. For more elaborate Compiz features, like wobbling windows, users can select the Extra option on the Visual Effects tab of the Appearance Preferences dialog.”

I remember Beryl, those were fun times.

Different desktop but KDE still has the wobbly windows as an option, I enabled them out of nostalgia recently.

Yeah, I worked on that but I didn't think that would count since it was a distro, not a desktop environment. In that case Novell shipped compiz in 2006 so even earlier.

macOS had one in 2000. Windows shortly thereafter.

What?

MacOS in 2000 was still old MacOS, with no compositing at all. The NeXT derived version of MacOS was still in beta, and I tried it back then, it was very rough. Even once OSX shipped in 2001, it was still software composited. Quartz Extreme implemented GPU compositing in 10.2, which shipped in 2002.

Windows finally got a composited desktop in Vista, released in 2007. It was GPU accelerated from day one.