From https://bugs.launchpad.net/catfish-search/+bug/1567787 catfish crashed with PermissionError in write(): [Errno 13] Keine Berechtigung: '/home/username/.config/catfish/catfish.rc'
Sean Davis referenced this bugreport in commit 7acb5b2863eab7d620b4401b64776bedf91b7839 Handle permission errors in settings handler (bug #14488) https://git.xfce.org/apps/catfish/commit?id=7acb5b2863eab7d620b4401b64776bedf91b7839
Fixed in the above commit.