See
https://github.com/jordansissel/xdotool/issues/346
for details.

--- a/xdo.c
+++ b/xdo.c
@@ -121,7 +121,6 @@
   // Try to detect XWayland and warn the user about problems.
   if (appears_to_be_wayland(xdpy)) {
     fprintf(stderr, "The X server at %s appears to be XWayland. Unfortunately, XWayland does not correctly support the features used by libxdo and xdotool.\n", display);
-    return NULL;
   }