Screen mirroring suddenly stop reaching Apple TV

Unfortunately, not everything can be screen mirrored to Apple TV (3rd generation).

• Select content providers block their content for AirPlay/Screen Mirroring in general for all models (e.g. Netflix).
• Select content providers will only AirPlay to AirPlay 2-compatible devices, which the 3rd generation is not (e.g. HBO Max).
• Select content providers will only allow AirPlay with certain plans (e.g. HBO Max).
• Select content providers stream video with specifications that may not be compatible with AirPlay by making no effort to be compatible (e.g. some web videos).

In general, see the content provider’s website on details for AirPlay compatibility. If they list nothing about it, then it is hit-or-miss.

So what type of content (from which content provider) were you trying to stream?

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Verify that the Apple TV box has its function for AirPlay receiving turned on. Settings﹥AirPlay﹥

Verify that the Apple TV box is activated/​registered with your Apple ID. Else AirPlay may not work because of that.

Use AirPlay to stream video or mirror the screen of your iPhone or iPad - Apple Support

If screen mirroring or streaming isn't working on your AirPlay-compatible device - Apple Support

Me, too. I've been daily screen mirroring my iPhone, iPad, and Macbook to my LG TV, multiple times daily for over a year. Then all of a sudden, on Tuesday they all stopped mirroring. I thought the problem must be on my TV since it persisted across multiple devices, but now that I see this, I'm wondering. All devices have been unplugged, restarted, reconnected to the network, and tried on a different network, etc. multiple times. No problem with either network connection. All are on the same network, and the TV shows up under the screen mirroring options, proving, I guess, that they're both connected to the same network, but when I click it, it just says "unable to connect." ??? Devices will screen mirror one another, just not the TV.