All streaming services are limited to Dolby Digital Plus 7.1 with or without Atmos metadata. It is a bandwidth issue. Even if the device supports lossless, the stream will be lossy. So, a TV's built-in apps or a connected streamer will deliver lossy streams while a connected disc player/game console can deliver a lossless multi channel signal to the TV that can then be sent from the TV via eARC to a receiver. ARC will handle the lossy stream well enough, but the lossless audio from a player would be lost and a lossy 5.1 signal would be output to the receiver instead.