Use legacy iTunes 12.6.5 + .ipa files from trusted archives (risky, requires jailbreak in some cases).
：这要求 App 的开发者仍然将旧版本保留在 App Store 服务器上。Apple 和许多第三方开发者不再在服务器上保留较旧的 App 版本，因此并非所有 App 都能通过这种方式获取。
Functions flawlessly for viewing, highlighting, and signing PDF documents. ios 9.3.5 compatible apps list
Excellent for streaming live AM/FM and internet radio stations globally.
If you want, I can produce:
If you try to download an app and see a "not compatible" error, use these verified methods to find a working version:
Keep it on your nightstand loaded with books via Kindle or Apple Books. Use legacy iTunes 12
Go to Settings > General > Background App Refresh and turn it off completely.
Excellent for streaming live global radio stations. Essential Tips to Keep iOS 9.3.5 Running Fast ios 9.3.5 compatible apps list