This is most likely an app+region+specific model provisioning issue: Prime & Now TV (and possibly others) may not be 4K/HDR/Atmos provisioned for the 3830 in the UK.
Some apps/service require that each and every different model (e.g. 3830) of a platform (e.g. RokuOS) be explicitly provisioned for 4K/HDR/Atmos VOD and/or Live (usually separately)
(Prime on the 3830 is (mostly) provisioned for 4K/HDR/Atmos VOD in the US - Live HDR10 (e.g. NFL/sports) support isnt provisioned for any RokuOS devices/models in the US).
You'll (and others) need to directly contact Amazon UK for Prime and NOW/Now TV for Now about specifically provisioning the 3830 for 4K/HDR/Atmos for their respective apps/services.
(This was an issue for 3830 and some apps/services in the US until very recently: Peacock & Vudu were not provisioned for 4K/HDR/Atmos until the last few weeks - the 3830 was released in May)
Prime considerations:
Keep in mind that the Prime app uses a 720p UI on ALL RokuOS devices/models (except for the 4850 - Ultra 2024, which uses a 1080p UI) regardless of region or being provisioned for 4K/HDR/Atmos playback - the app's UI looks blurry because its 720p, but that is separate from the stream/playback quality.
You can check the Prime app's stream/playback quality by accessing the Developer OSD via remote button sequence: L, R, U, D, U, D then R, L, U, D, then check the "Video Quality" box for bitrate+resolution details.
Finally, sometimes the Prime app limits/lowers the streaming playback resolution to 1080p when the Prime app's Autoplay setting is disabled - try turning Prime's Autoplay = ON if you notice streaming quality is limited to 1080p.
Otherwise if this isnt the 720p UI issue, and Autoplay is enabled, then you'll need to contact Amazon UK as previously stated.
NOW/Now TV considerations:
Since NOW/Now TV is essentially a UK-only venture (aside from Xfinity customers in the US, and only available via Xfinity service/app) I cant comment on its 4K/HDR/Atmos/etc provisioning process/status, and you'll have to contact NOW/Now TV directly about provisioning the 3830 for 4K/HDR/Atmos/etc.
