Full policy: https://gametome.app/privacy (section "Browser extension").

When connected, and only on Steam, IGDB and GOG game pages, the extension sends the game's identifier to gametome.app to show its status in your backlog, and sends the status you choose. It does not read other pages or your browsing history. The personal code that connects it is stored only in your browser; GameTome keeps only a hash of it, its creation date and its last use, until you revoke it in Settings or change your password. No data is sold or shared with third parties.