I think Xwayland 22.1 introduced a regression caused by the libxcvt transition.
I have a very particular use case that exposes this regression: a fullscreen ("rootful") Xwayland window running a traditional X window manager (specifically, JWM), under a wlroots-based compositor. The problem can be reproduced with either Cage or dwl, and wlroots 0.15.1.
There's a 6px gap on the right of the panel drawn by the window manager, although it is possible to place X windows over this gap:
This probably means that the Xwayland window is 1366x768, but the X applications inside it think it's 1360x768.
Unsurprisingly, xrandr says the display mode is 1360x768, although wlr-randr reports the correct resolution of 1366x768.
If this is indeed a regression, it's a re-introduction of https://bugs.freedesktop.org/show_bug.cgi?id=99574. Maybe libxcvt isn't the right place for this magic if, which was originally in xwayland-cvt.c.