Index: /trunk/src/VBox/Additions/darwin/Installer/VBoxGuestAdditionsKEXTs/postflight
===================================================================
--- /trunk/src/VBox/Additions/darwin/Installer/VBoxGuestAdditionsKEXTs/postflight	(revision 87878)
+++ /trunk/src/VBox/Additions/darwin/Installer/VBoxGuestAdditionsKEXTs/postflight	(revision 87879)
@@ -61,6 +61,12 @@
 done
 
+MACOS_VERS=$(sw_vers -productVersion)
+
 echo "Updating kernel cache (should trigger loading of new modules)."
-touch "/System/Library/Extensions/"
+# /System/Library/Extensions is readonly in Catalina and later,
+# so touch returns always false on these systems   
+if [[ ${MACOS_VERS} != 11.* ]] && [[ ${MACOS_VERS} != 10.15.* ]]; then
+    touch "/System/Library/Extensions/"
+fi
 kextcache -update-volume / || true