The edition matters
A title may have different editions across viewing services. Check the quality label on the offer you select. A high-resolution poster on PrimeFlix does not establish that the video is available in 4K.
Match the screen and connection
A stable HD or 1080p stream can be more comfortable than a higher setting that repeatedly buffers. Use the player's quality control if available and compare the result on the actual screen rather than choosing by the largest number alone.
Resolution is not the whole picture
HDR, compression, display settings and the source transfer can affect the image. A dim picture is not always a resolution problem. Check the service's supported settings for your device before changing several display controls at once.
Sound deserves the same check
Confirm the correct output and audio track. If you connect a laptop to a television, the picture and sound may initially use different devices. Test them before the film gets underway.