Yeah, it's confusing. It's been confusing for years.
Most likely what you read is that stock Ubuntu (the version with the GNOME desktop) has switched to Wayland in 22.04. What stock Ubuntu does is not necessarily indicative of what Ubuntu MATE does. Like @ricmarques said above (actually what @Wimpy said in the 22.04 release notes), the MATE session as it stands cannot run on Wayland without some semi-unofficial "patches". @wmww is the main developer who pushes MATE development regarding Wayland forward, and he's got a number of modified MATE programs that, when used in conjunction with most of the normal MATE applications (which individually support Wayland now), can be used to start a Wayland-based MATE session. I've never tried it myself, but I hear it mostly works. (Should you try it, beware. As with any "beta-quality" software, it's possible it'll crash upon you spontaneously.)
As for the stock Ubuntu side of things, that's confusing because Ubuntu has switched back-and-forth between X11 and Wayland several times since 2017 (if I recall correctly). The following timeline is according to my own (flawed) memory:
- Ubuntu first deployed Wayland as an option when you log in, but not the default, in version 17.10.
- In 18.04 the option was not even included by default.
- In 18.10 the Wayland option was included again, and I think it was even the default.
- But users complained that applications didn't always work right under Wayland, and the cursed Nvidia drivers were unavailable for Wayland (as if you'd actually want them anyway
). So Ubuntu switched back to X11 by default but kept Wayland as an option for the 19.04 and 19.10 releases. - 20.04 didn't even have Wayland as an option.
- I know for sure that 21.10 didn't have Wayland as even an option, because I was quality assurance testing Ubuntu MATE during that release cycle and I was trying to figure out why Ubuntu MATE's installer had so much trouble communicating with the screen reader. (I had to dig pretty deep to find the answer to that one -- I initially thought it was a difference between Ubuntu using Wayland and Ubuntu MATE using X11, but I figured out that both used X11.)
And, if you believe this article from gHacks (https://www.ghacks.net/2022/04/21/ubuntu-22-04-lts-with-gnome-42-and-wayland-as-the-default/), Wayland is the default on stock Ubuntu now, and it looks like it's the first LTS release to hold that achievement.
However, let me make this clear: Officially, without extra patches, the whole MATE desktop doesn't run on Wayland yet. I know that because I'm a member of the MATE development team. Sorry.
OK, enough of my diatribe for one post.