Ok, yes with ionic cordova build android --prod I have an app-debug.apk file that I can install on my phone.
Thank you.
It is strange that with the same command "ionic cordova build android --prod --release" we have two different file. I have an “unsigned” file that I can’t install.
However, for testing the app, at this moment, I can use the debug version.
Maybe it does not make sense to have a release version not signed.