Read the edition, not just the label
HD can describe more than one resolution. Full HD commonly refers to 1080p; consumer UHD 4K uses a higher-resolution image. The edition available through your selected service determines which options you can actually choose. Your plan, device and connection may also limit them.
A stable picture can be the better picture
If the video repeatedly pauses at its highest setting, try a lower quality in the player when offered. A connection can be fast but inconsistent. Pause large transfers and test again before changing every preference. Adaptive playback may lower or raise resolution automatically as conditions change.
4K is not the same as HDR
Resolution describes the image dimensions. High dynamic range concerns how a supported edition and display represent brightness and colour. One label does not automatically establish the other. Inspect the chosen app's edition information and device requirements.
Settle the room too
Glare, seating distance and audio clarity can matter as much as a resolution number. Start the film with comfortable captions and sound, then adjust only what needs attention. Continue to device help for TV and casting questions, or playback help when the player shows an error.