In 2014, the Debian project cited accessibility [1] as a main reason to offer Gnome as the default desktop. Since that was over 9 years ago, a lot could have changed. However, observing that Gnome is generally the most well funded Linux desktop, and is sponsored by/the default for Red Hat Enterprise Linux [2] that has large incentives to meet government accessibility regulations, there's a good chance it is still ahead.
[2]: It is also the default on other enterprise Linux vendors, such as Ubuntu (albeit customized) and even major KDE supporter SUSE uses Gnome Classic mode as the default for SUSE Linux Enterprise Desktop
There generally has been a major regression for both GNOME and KDE with regards to accessability with the switch to Wayland IIRC. Mostly due to the strict separation of apps and not being able to snoop eachothers windows by default.
Tho there have been major works sponsored/supported by GNOME/STF to improve the entire accessibility stack used in the Linux userspace https://www.youtube.com/watch?v=w9psDfEFf9c
[1]: https://salsa.debian.org/installer-team/tasksel/-/commit/dce... (they cited systemd integration too, but that situation has probably changed a lot since then)
[2]: It is also the default on other enterprise Linux vendors, such as Ubuntu (albeit customized) and even major KDE supporter SUSE uses Gnome Classic mode as the default for SUSE Linux Enterprise Desktop