As noted by other commenters, there are several compositors available for Wayland (essentially the bit that actually implements Wayland).
Some are developed independently of any particular desktop environment--like wlroots, labwc, hikari, etc--but some are part of a larger project, such as mutter and kwin (GNOME and KDE, respectively). Most of the time you install some sort of GNOME/KDE + Wayland distro, you'll usually also end up with their compositors, and thus potential quirks specific to their implementations.
GNOME's implementation in particular has historically caused a lot of drama relative to some of the others -- be it due to purely accidental, broken support for something, or sometimes intentional opposition to a particular concept that many applications rely/used to rely on, like server-side window decorations [1].
The accidental issues that come with fragmentation of the ecosystem and the intentional decisions by different compositors to not support particular extensions/whatever, like the aforementioned, can cause a fair bit of pain for developers of end-user programs.
Users who may be totally unaware of the inherent differences between Wayland and X, who may not know that different compositors exist, who may not even know they are running Wayland, etc, inevitably run into strange issues, and then, understandably, file bug reports.
This can get old quickly under normal circumstances. But I imagine it sucks even more when you're maintaining software that is relatively understaffed given its importance. Outside of PCSX2, mpv would be a good example:
- It's incredibly popular software on its own, being probably the most popular open-source, cross-platform mediaplayer after VLC.
- It's also embedded and used as a base for other applications on a wide variety of systems, ranging from other open-source players that try to integrate more tightly with a given platform--e.g., IINA (macOS), mpv.net (Windows), etc--to proprietary, commercial software, such as a variety of Android players and, importantly, Plex, which uses mpv as the default backend on at least tvOS/iOS/iPadOS.
- It's software that needs to deal with pretty low-level graphics and audio stuff, so it's inherently a bit complex, and the available pool of potential contributors shrinks.
- It tries to be as lightweight as possible and allow for easy embedding into other applications and porting to different systems, so it has several things working against it:
-- It's mostly written in C, making it very easy to build and embed anywhere, but not only is C not the sexiest language in 2023 to many, it's also a hard language for someone without a good grasp to write safe, quality code, particularly for something like mpv.
-- It doesn't try to enforce a particular rendering backend--e.g., OpenGL, DirectX, Vulkan, Metal, software, etc--nor a particular UI toolkit. Again, great for someone building on top of it. But it makes things like the change from server-side decorations to client-side significantly more annoying / potentially fundamentally incompatiblew ith the project goals.
mpv sits in that perfect anti-goldilocks zone:
It's important enough to be a problem if it were to disappear, yet unlike the Linux kernel, not quite important enough to have the funding and hoardes of patches despite the project complexity. It's also low-level enough to need to worry about every display server and platform on the planet, yet not low-level/general enough to have a say in the design decisions (e.g., Wayland membership, I believe, is pretty much limited to compositors and UI toolkits - like QT/GTK).
All of that, and probably more, adds up to maintaining a surprisingly important, difficult project with relatively few developers but likely many millions of users, many of whom may not even know you exist; it's thankless yet important work.
As a result, unsurprisingly, in addition to the infamous locale rant [2] (unrelated to Wayland), mpv used to have a pretty spicy wiki section entirely dedicated to GNOME's Wayland implementation:
- https://github.com/mpv-player/mpv/wiki/FAQ/ddcbe1b88a99d2568... (2020)
This section still kind of exists, but it has been toned down a fair bit now that certian issues have been addressed [3]; it now mainly focuses on a couple of specific GNOME issues directly and more broadly addresses NVidia's poor Wayland support relative to some other vendors.
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[1]: https://gitlab.gnome.org/GNOME/mutter/-/issues/217
[2]: https://github.com/mpv-player/mpv/commit/1e70e82baa9193f6f02...
[3]: https://github.com/mpv-player/mpv/wiki/FAQ/a70c96040ad4fa374...