This and skip credits are the same feature. This minimizing is because whoever owns the server ran credit detection for that particular library. And some clients, instead of simply displaying a “Skip credits” button, will instead shrink the window to this “up next” feature (I really dislike it).
If you control the server, you can disable credit detection on a per-library basis by editing your library, or server-wide by disabling it in Settings → Library → Generate credits video markers dropdown and picking never.
I… don’t think there is anything you can do about it if you view content owned by someone else who has enabled credit detection. Being logged into an account with Plex Pass will use credit markers if they exist. A quick press on the “OK” button will quickly maximize any movie that shrank like this.
