I doubt that. Netflix has an app on TVs as old as 8-10 years now. SoCs in such TVs aren't enough to decode AV1. They're stuck with H.264 for a long time.

I can't figure out an answer to why they'd do this. They're still supporting their custom Chromecast "receiver" app (for now?), which is a standard HTML app. But now they're detecting the Chromecast-capable device model, looking it up in an allowlist, then conditionally showing the device in the Netflix App's Cast UI.

This would mean if you have a new device and an old device in the same network the Netflix app might show only your old device! What?

Maybe I'm misunderstanding what they've done here?

Nah, that's more "we can't get ad injection working on the old Chromecast client" because it still works on early Chromecasts for ad-free plans.