There's more detail in the iPhone battery information page.

Testing conducted by Apple in August 2021 using preproduction iPhone 13 mini, iPhone 13, iPhone 13 Pro, and iPhone 13 Pro Max units and software, subscribed to LTE and 5G carrier networks. Video playback consisted of a repeated 2-hour 23-minute movie purchased from the iTunes Store, tested with stereo audio output. Video playback (streamed) consisted of a repeated 3-hour 1-minute HDR movie purchased from the iTunes Store, tested with stereo audio output. All settings were default except: Bluetooth was paired with headphones; Wi-Fi was associated with a network; the Wi-Fi feature Ask to Join Networks, Auto-Brightness, and True Tone were turned off.

https://www.apple.com/iphone/battery.html#:~:text=Video%20Pl...

Year after year, real world tests show that Apple’s battery estimates err on the conservative side. Enough that we should stop seeing comments like this and yet here we are.

What is meaningless is raw specs on their own. Your massive phone battery is useless if you’re using it to power a 1000W space heater.

While the real world tests after release essentially always bear out Apple’s battery life and performance estimates as reasonable and fairly typical, I don’t fault anyone for generally holding product claims with skepticism. Apple is somewhat unique in reporting these values honestly.