The edition sets the limit
The letters HD do not establish the resolution of every film in the catalogue. Check the viewing edition, plan and device. A source available in one format cannot gain genuine detail simply because the screen supports a larger number of pixels.
1080p commonly means 1,920 by 1,080 pixels. Consumer 4K UHD commonly means 3,840 by 2,160. HDR describes a wider brightness and colour range, not another name for resolution. Compatibility matters for all of them.
Start with a natural picture
Preserve the film's framing rather than stretching it to remove black bars. Grain, deep shadows and muted colours can be intentional. Try a neutral display mode before adding sharpness or saturation to compensate for a style you are not used to.
Choose steadiness when the connection struggles
If the service provides quality controls, reduce the resolution temporarily and see whether playback settles. A consistent picture is usually easier to enjoy than a sharper image that pauses repeatedly. Adaptive quality, where supplied, is controlled by the player.
For a phone, consider battery and mobile data as well as resolution. For a television, test the image from your normal seat. Device choices and subtitle settings can matter as much as the resolution label.