Start with the available edition
Open the viewing options for your title and country. The service determines the video edition, resolution and any plan requirement. Poster size and background artwork on Zmov do not indicate whether that edition plays in HD or 4K.
Resolution is one part of the picture
1080p can be an excellent fit for a laptop or a smaller television. A supported 4K edition can reveal more detail on a larger display. Compression, display settings and the source photography still matter. A larger resolution label does not guarantee that every scene will look sharper or brighter.
A steady image beats constant interruptions
Try automatic quality if playback repeatedly pauses. Adaptive video delivery can adjust to connection changes where the player supports it. On a shared network, another large transfer may reduce the bandwidth available to the film. Compare the same scene after one change instead of altering every setting together.
Dark scenes and dialogue
Check the television's picture mode if shadow detail is difficult to see, but avoid assuming that maximum brightness is the answer. For quiet dialogue, check the audio output and available stereo or dialogue settings separately. Image and sound problems can happen together without having the same cause.