違うか
古い対象外のモデルも低解像度で使用できる場合がある
みたいな感じかな

Available on MacBook Pro (2018 and later), MacBook Air (2018 and later), iMac (2019 and later), iMac Pro (2017), Mac mini (2020 and later), Mac Pro (2019), iPhone 7 and later, iPad Pro (2nd generation and later), iPad Air (3rd generation and later), iPad (6th generation and later), and iPad mini (5th generation and later).

Older iPhone, iPad, and Mac models may share content at a lower resolution to supported Mac models when “Allow AirPlay for” is set to “Everyone” or “Anyone on the same network” in Sharing preferences.