I am not tried webpacker 4 on production but made an example app with webpacker version 4. The rake -P command works and bin/webpacker command works as well.

You can check the example app here.

November 10 Update:

If you have no yarn installed in your operating system then you need to specify aWEBPACKER_NODE_MODULES_BIN_PATH variable to avoid yarn call in webpacker internals. Here you can see one option how you can implement it.