Original ROM now supports call recording with the Google Phone app, it's rolling out for beta users. However it's manual still, you need to press to record everytime you call someone.
You can also use Google Phone app on MIUI.EU ROM, but the only way to make it work 100% that i've found was downloading Truecaller app and starting setting it up. Instead of setting Truecaller as the default for all options, choosing Google Phone and after it's set, just uninstalling Truecaller. Didn't find a way to set Google Phone as default without any apps.