For some reason, the new Express 4K units don't exactly behave the same as the older Ultra, Streaming Stick +, Premiere Plus and Premiere models where options key override is not working when a stream is playing, even if not full screen.
Under enableUI, https://developer.roku.com/en-ca/docs/references/scenegraph/media-playback-nodes/video.md states:
If set to false, most of the Video node user interface will not be shown, and the application is expected to implement the UI. The one exception is the closed-caption dialog, which always appears when the video is playing fullscreen and the user presses the Options (*) button
The above is the case with most Roku models. However when using an Express 4K unit, the closed-caption dialog ALWAYS appears when video is playing, even if it's not fullscreen and onKeyEvents are ignored when pressing the options button.
Also tried setting the new video.allowOptionsKeyOverride property to "true" which has no effect so it seems that this has to be fixed at the firmware level.