In , select multiple proxies. Right-click → "Enable rotation" . Set interval (e.g., 10 minutes) or rotate after X failed downloads. JD2 will cycle through the list top-to-bottom.
JD2 does not natively support proxy authentication via NTLM or Kerberos. Only Basic Auth (user:pass) or no-auth are allowed. Jdownloader2 Proxy List
There are several sources where users can obtain proxy lists for JDownloader2: JDownloader2 Proxy List: A Comprehensive Report 3