Use content matching where appropriate
Apple documents Match Dynamic Range for preserving a source’s original dynamic range on supported equipment. Its video guide also provides output and HDMI checks. Use the current model-specific settings rather than applying an arbitrary “always force HDR” rule.
The complete HDMI chain matters, including any receiver or soundbar. A setting available on the Apple TV is not proof that every connected component accepts it reliably.
Compare with known material
Keep the player, video and viewing environment constant while testing a relevant output setting. Note whether the issue occurs in every app or only one source. Avoid changing brightness, range, resolution and source together.
If only one item looks wrong, retain its actual format and application details. If all applications are affected, the system/display path becomes a more relevant starting point.
Describe the result accurately
State the source information and output mode separately. A better-looking picture after a display change is a useful observation, but it is not evidence that the source gained native detail or that every HDR format has been tested.