How to reproduce:
1. Open the attached 'ReproProject.zip' project
2. Switch Platform to iOS in Build Settings
3. Build for iOS and open the Xcode project
4. Deploy Xcode project to an iOS device with a notch

Expected result: Screen.safeArea method takes notch into account and returns: x: 0 y: 0 width: 828 height: 1636 values (iPhone XR)
Actual result: Screen.safeArea method takes notch into account and returns: x: 0 y: 0 width: 828 height: 1792 values (iPhone XR)

Reproducible with: 3.2.16, 3.2.17(2019.4.17f1, 2020.1.17f1, 2020.2.0b14, 2020.1.0a10)
Could not test with: 2018.4.30f1 because of the XR Management package errors

Reproducible with:
iPhone XR (iOS 13.4.1)
VLNQA00001, Google Pixel 2 (Pixel 2), Android 11, CPU: Snapdragon 835 MSM8998, GPU: Adreno (TM) 540
----------, Oneplus OnePlus 6 (ONEPLUS A6003), Android 10, CPU: Snapdragon 845 SDM845, GPU: Adreno (TM) 630
VLNQA00331, Huawei P20 lite (ANE-LX1), Android 9, CPU: HiSilicon Kirin 659, GPU: Mali-T830
VLNQA00231, Huawei HUAWEI Mate 20 Pro (LYA-L29), Android 9, CPU: HiSilicon Kirin 980, GPU: Mali-G76
----------, Google Pixel 3 XL (Pixel 3 XL), Android 11, CPU: NOT FOUND, GPU: Adreno (TM) 630

Not reproduced with:
VLNQA00334, Xiaomi Mi A3 (Mi A3), Android 10, CPU: Snapdragon 665 SM6125, GPU: Adreno (TM) 610 (safe area: w:720 h:1507)
VLNQA00229, Oneplus OnePlus6T (ONEPLUS A6013), Android 9, CPU: Snapdragon 845 SDM845, GPU: Adreno (TM) 630 (safe area: w:1080, h:2261)

Notes:
- Screenshots of the issue are attached in Edit
- In order to see correct results, disable 'Initialise XR on Startup' option in Project Settings
- As a conclusion of the discussion below, the correct fix is actually to update the documentation to reflect the fact that these values are not available immediately at startup.