sxmo: disable xwayland

hosts/modules/gui/sxmo/default.nix

@@ -307,7 +307,12 @@ in
             # these could be added, but i don't see much benefit.
             font = "pango:monospace 10";
             mod = "Mod1";  # prefer Alt
-            # xwayland = false;  # disable to reduce RAM usage. N.B.: xwayland is needed for electron apps!
+            # about xwayland:
+            # - required by many electron apps, though some electron apps support NIXOS_OZONE_WL=1 for native wayland.
+            # - when xwayland is enabled, KOreader incorrectly chooses the X11 backend
+            #   -> slower; blurrier
+            # - xwayland uses a small amount of memory (like 30MiB, IIRC?)
+            xwayland = false;
             workspace_layout = "tabbed";
 
             brightness_down_cmd = "sxmo_brightness.sh down";