As in subject, I tried several apps/configurations but It seems Android 11 doesn't allow to record incoming voice.
Did you find a working app or a workaround to let it work?
As I said, I can't root my Samsung S21, neither can use speakerphone when receiving calls.

Any help is really appreciated.

Samsung offers call recording within the Samsung call app. It`s very basic, but it works. It might be blocked if you`re located in an area where the law doesn`t allow call recording.

Thank you, I tried to enable Samsung built-in recorder following some online guides since I never noticed such an option, but it seems I'm on a "forbidden recording area". What's fun is it isn't forbidden by law to record, but only to go public with the recording if the subject involved don't formally agree to make it public. So it's perfectly legal for a private use. Maybe at Samsung aren't aware of this...