KWin
As 470535 – noborderrule=2 doesn't work on Wayland, does on X. demonstrates, there is a (recently much) neglected KWin rule called “No titlebar and frame”, which, when set to “Force” and “No”, forces server-side window decorations even for windows which instruct the display server to not display them.
This feature was the reason I transferred to KDE Plasma from GNOME rather than going back to Windows 11 when I realized how much I disliked that DE. However, as the title of the aforequoted issue alludes to, this feature doesn’t work in Wayland. Although I find it such an important accessibility feature, I used to only imagine that this is due to lack of interest. After all, accessibility features are generally solely used by a subset of users.
However, when it was marked as a duplicate of 452240 – wayland: "No titlebar and frame" rule doesn't force SSDs on Wayland recently, which itself is marked as RESOLVED INTENTIONAL, I realized that this was somehow intentional. To understand why, I read 452240 – wayland: "No titlebar and frame" rule doesn't force SSDs on Wayland, which explains that the window border would need to render outside the GTK window border on GTK4 windows, so this isn’t desirable anymore.
That isn’t rationale for dismissing an accessibility feature, but regardless, as 479372 – Native window border renders far past boundaries of GTK 3/4 window border when noborderrule=2. demonstrates, that’s literally what already occurs on X11, yet the feature remains operative there:
Additionally, one can enable the feature on Wayland, and it merely silently doesn’t work. I don’t believe that this is how an accessibility feature should be treated!
I’ll soon have no OS nor DE which provides this functionality when most distributions lose support for X11, because neither Windows 11, macOS, nor GNOME 42 provide this functionality. I don’t want to use X11 regardless, but I’m forced to.
Plasma
Even more strangely, as Any idea why my plasmashell windows are missing a window border? (cited in 476996 – Allow window border to render on plasmashell windows too.) demonstrates, this is deliberately prevented from applying to plasmashell. I’ve not heard any rationale for this, and I have no idea why, because I’ve quite prominently asked. At the very least, the issue shouldn’t have been closed until the reason had been explained!
One of the principle concepts of Plasma is that the user ultimately has control of their system. I’m aware that that generally causes unnecessary complexity which is a significant burden on the developers, but in this case, plasmashell itself is the example of unnecessary complexity. If the Plasma developers believe that by default this rule shouldn’t apply to plasmashell (which is somewhat reasonable if you’re using the rule for cosmetic reasons, I suppose) then create a default KWin ruleset excluding plasmashell! Why hardcode that it cannot have window decorations?!
Conclusion
I’ve posted this greivance publically because things like https://www.reddit.com/r/Windows10/comments/hpwx06/does_anybody_know_if_you_can_force_disable_csd/?utm_source=share&utm_medium=web2x&context=3 demonstrate that I’m not the only one with this concern, even if for others it’s a primarily cosmetic issue. However, that’s not solely why. If anyone can provide useful steps toward remediating this issue (which don’t necessitate I use another window manager, because I don’t think I’d ever manage that, and those others I care about certainly wouldn’t be able to) I’ll be incredibly grateful.
Many thanks.