or substituted its own SSH host keys,

why would the backdoor do that? It would immediately expose itself because every ssh client on the planet warns about changed host keys when connecting.

For context, LDAC is one of the few wireless audio codecs stamped Hi-Res by the Japan Audio Society and its encoder is open source since Android 8

LDAC is great, but simply stating that the encoder is “open source” is quite misleading (while technically correct). The codec is owned by Sony and heavily licensed. It’s a savvy business move of Sony to make the encoder free to use though, so everyone else can support their standard while charging manufacturers who want to integrate it into their headphones.

If we want a really free and open high quality codec, we should push for opus support via bluetooth