Uploads come from each channel's public feed. Data API not connected
Every card is a title, thumbnail and link that opens the video on YouTube. Nothing is embedded, downloaded or re-hosted, and each feed carries only a channel's most recent uploads, so this is not a full back catalogue. Searching YouTube from inside the app, playing video in an embedded player, and channel subscriber data all need the official Data API, which is not configured.
Following a channel here is an Auto Collective action. It does not subscribe your YouTube account.