For the FireTV 4K Max, passthrough for TrueHD + Atmos and EAC3 + Atmos works with the current 10.5 release.
Amazon has a longer update approval process than Google. As a result, FireTV devices are usually a release or two behind what is current on Google.
If desired, you can download 10.5 from the announcement thread and sideload it on the Firestick. Use the FireOS Devices version. Sideloaded apps do not auto-update, so you’ll have to delete & re-install from Amazon store to get auto-updates back.
