Check the offered edition
Quality belongs to the actual video, not the poster used to identify it. Open the available offer and check what that service supports for the title, device and plan. A 4K television can display lower-resolution material too.
When the picture starts soft
An adaptive player can begin at a lower quality while it assesses the connection. Give it a short opportunity to settle, then inspect any quality menu. If a high setting keeps buffering, try a lower supported one and compare the result.
Sharpness is not everything
Compression, source condition, motion and lighting in the room all affect the experience. A stable 1080p edition can be more comfortable than a higher setting that repeatedly stalls. An older production's restored edition may also differ from another offer of the same film.
Do not change every setting together
Start with the player's options, then check connection strength and competing network activity. If only one title looks wrong, compare another before resetting the device. Playback help separates quality changes from loading and audio problems.