A sharp poster is not a video-quality label
The artwork on a movie page is separate from the video edition. To watch in HD, 1080p or 4K, check the offer, service plan, device and player. A film can have different available editions in different countries.
When Auto is useful
Adaptive bitrate playback adjusts delivered quality to current conditions where the player supports it. An image may begin softly before improving. If the alternative is repeated stops, a steady lower setting can be the more comfortable choice.
4K and HDR are different
4K concerns resolution. High dynamic range concerns brightness and colour handling on compatible equipment. An edition may support one without the other. Check the selected app and screen rather than treating the terms as a single badge.
Try a controlled comparison
Use the same short scene after each adjustment. Check the player setting, then compare another supported device or connection if available. Do not change resolution, browser, audio output and network at once; you will lose track of what improved the picture.
For pauses or a black screen, use playback troubleshooting. For text clarity, use subtitle settings.