I forgot to forward the motion events for X11 in gtk4.
Created attachment 400729 [details] Patch
Thanks for the patch. If this patch contains new public API please make sure it follows the guidelines for new WebKit2 GTK+ API. See http://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Committed r262372: <https://trac.webkit.org/changeset/262372>