The short explanation
Streaming devices read the capability data and configure their output accordingly: resolution, frame rate, HDR format, audio format. Many keep a record of which capability sets they have already tested successfully.
Where you run into it
The memory explains a common surprise: change the EDID and the device wants to retest Dolby Vision, then never asks again for that same EDID. Not a fault — it is the cache working as designed.
Audio settings are the other frequent cause. A format override switched on to solve an older problem will keep the device on the older format, and no amount of EDID work will change that until the override is turned off.
App-level settings matter too: a streaming service's own audio quality setting can cap what you receive regardless of the hardware.
How the DR HDMI 8K handles it
The DR HDMI 8K's manual carries a dedicated Apple TV 4K FAQ for precisely these behaviors, and the EDID controls let you present a specific capability set and then force a re-read with ISSUE HOTPLUG. If Atmos or Dolby Vision is missing, comparing the advertised capability against the device's own settings usually separates the two causes in a minute.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.