Understand what Popout changes
Opera documents a movable, resizable video window with its own playback controls. This changes how a supported web video is displayed; it does not install a standalone player or create a separate subscription session.
The original browser tab remains relevant. Opera’s help states that media can continue there after the floating window is closed. If sound continues unexpectedly, inspect the host tab and its controls rather than assuming an unknown device is using the account.
Use the supported service first
A browser feature cannot make every website or media format compatible. Use the service’s genuine supported web player and platform requirements. A private playlist address alone is not necessarily a playable web page.
If the Popout control is unavailable, establish whether that particular video/site supports the browser feature. A missing floating-window button is different from video that refuses to start at all.
Keep troubleshooting narrow
Record whether playback fails in the original tab, only in Popout or after moving between windows. Keep the browser version and operating system with the result. This can separate a display/control issue from an authentication or source problem.
Use normal publisher/browser troubleshooting. Do not install a codec pack or extension from an unrelated page merely because it promises to repair every stream.
Stop the intended session
Before leaving a shared computer, use the actual playback controls and check the original tab. Closing a display surface and stopping a media session are not always the same action. Keep account sign-out and any stored credentials appropriate to the shared-device setting.