I just upgraded to Webpacker 6.0.0.beta.5 and this error came up.
ActionView::Template::Error (undefined method `javascript_packs_with_chunks_tag' for #<ActionView::Base:0x0000000000fcf8>
Looks like this method was removed in the latest Webpacker version because both javascript_pack_tag and javascript_packs_with_chunks_tag did the same thing. Here's the PR https://github.com/rails/webpacker/pull/2895
To solve this, just rename javascript_packs_with_chunks_tag to javascript_pack_tag in all your files and you should be good.