When adding an indexer to Prowlarr, the indexer does not propagate immediately. If an immediate propagation is desired, a synchronization can be triggered by following the menu options: System→Tasks and then clicking the refresh icon next to the Application Indexer Sync option.

Setting up a proxy with Prowlarr is counter-intuitive and here are the steps necessary to set one up:

• Go to Settings→Indexers and add either a HTTP, Socks4 or Socks5 proxy,
  • Specify a "Tag" for this proxy.
• Now all the indexers that are added to Prowlarr should have the same tag added manually when the proxy was defined in Settings→Indexers.

Assuming that Prowlarr is set up to use Tor as a proxy, some indexer definitions can be converted to use the indexer onion address instead of the clearnet address in order to avoid random blocks due to Cloudflare prompting for CAPTCHAs.