“The Final Cut Camera app is a free download on the App Store, but if you want to use the live multicam feature, you need a Final Cut Pro subscription on a recent iPad ($4.99 per month).”
The camera app is free and runs on iPhones back to the 2018 XS. The multicam part needs Final Cut Pro 2 on an M1 or later iPad, plus $4.99 a month. Four angles means four Apple devices, all talking over Wi-Fi and Bluetooth. Apple gave away the camera and charges rent on the switcher.