Google has limited API for call recording to system apps in Android 6. But some developers have found workarounds to these limits and these workarounds worked till Android 8.1. But these workarounds will no longer work on Android 9 Pie, unless you have a rooted device.
Who affected? This change will affect all call recording apps on Android. So please don't blame develoeprs who can't provide you the functionality which is blocked by the system.
What can be done? Blocking call recording makes no sense to us. There are so many users who use this feature daily. Adding a special permission for third-party apps would be trivial for Google. They could even implement call recording API over Play Services, so we wouldn't need to wait till the next Android release.
Current workarounds for non-rooted devices Turning load speaker while in call Setting recording mode to Stereo and try to find the best suitable volume control values for your device (E.g. Tx: 50%, Rx: 800% for Pixel 2) Repeat important information during a call