I tried to install the zip from
this link to my libs folder to enable RAR5 support. In Jdownloader's options I can see that the Archive Extractor is "7Zip Binding Version: 15.09-2.01beta" but the archive menu is greyed out on the context menu for archive files, and archives are no longer being automatically extracted.
I am using Windows 8.1 and Java 8 Update 191. JDownloader2 has been updated to the latest version as of this post.