It's not something that Xwayland does but rather something that the window managers are doing. We cannot use None as an indication of focus loss because some other X11 WM are using it as a transient state when changing focus, and we don't want to translate it into more Win32 side focus changes that would cause additional requests and confusion. The Wayland compositor logic has been changed in the various MR listed in https://gitlab.winehq.org/wine/wine/-/merge_requests/8117.