Index: src/core/worker.cpp
--- src/core/worker.cpp.orig
+++ src/core/worker.cpp
@@ -367,7 +367,7 @@ Worker *Worker::createWorker(const QString &protocol, 
     const auto useThreads = []() {
         return qgetenv("KIO_ENABLE_WORKER_THREADS") != "0";
     };
-    static bool bUseThreads = useThreads();
+    static bool bUseThreads = false; // useThreads();
 
     // Threads have performance benefits, but degrade robustness
     // (a worker crashing kills the app). So let's only enable the feature for kio_file, for now.
