Optionally, if your extension is required to open an external URL for configuration or as a core functionality for the panel, list the URLs under Whitelisted Config URLs or Whitelisted Panel URLs. Linking to an external site for a video overlay extension is strictly prohibited.
“Extension Capabilities”
You are correct. Linking to an external site is “Panel” or “Config” only at this time
Note also:
Off-site linking:
Video-overlay extensions may not contain links of any kind.
Panel extensions must submit a whitelist of domains requested for off-site linking.
Off-site links must be related to the extension’s core functionality.
Off-site links may not refer users to sites that deliver functionality effectively similar to that available on Twitch.tv.
Under:
Under “Content Policies”