Hello, I faced the same issue as well. The Apollo for Reddit modded will not download. I also tried via Sideloadly and receive this error message,
"There was an issue during installation: 0: AppexBundleMissingClassOrStoryboard (Appex bundle at /var/installd/Library/Caches/com.apple.mobile.installd.staging/temp.BKowHh/extracted/Apollo.app/PlugIns/com.christianselig.Apollo.GL8GRRP462.AthenaWidget.appex with id com.christianselig.Apollo.GL8GRRP462.AthenaWidget does not define either an NSExtensionMainStoryboard or NSExtensionPrincipalClass key with a string value in the NSExtension dictionary in its Info.plist)"
Anyone have any ideas?