Screen Mirror from iPhone to TV
How can I turn my Panasonic smart tv into an AirPlay 2-compatible smart tv?
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You cannot turn it into an airplay compatible receiver at all. It either is or it isn't. It would need special hardware to be compatible and there's no way to magically add the hardware to a TV that does not have it.
If your TV is not Airplay 2 compatible, then you can connect a device such as Roku, Amazon Fire Stick, Chromecast, Playstation, Xbox or an actual Apple TV box and use that device's Airplay 2 compatibility to stream things to the connected TV.