At first, all my test machines would report errors because my mdm file was configured incorrectly. I configured PluginBundleID as the bundleid of the system extension, and then changed it to the bundleid of the extension container app. The same network filtering program implemented with the network extension would not trigger SIGPIPE in 10, 11, 13, and 14.6.1, but would still trigger SIGPIPE in 12.6.0 and 14.5.0. And on the machine without mdm, 12.6.0 and 14.5.0 would still trigger SIGPIPE.