This ROM uses the most GApps compared to any other AOSP ROM.
This is meant to duplicate the Pixel UI from Google's Pixel devices and hence the name.
But, even other ROMs such as Paranoid Android uses Google dialer, contacts and messages app.
You can disable the messages app and use any other instead. Same for Phone and contacts apps. But using proprietary MIUI system apps seems impossible without the MIUI framework. But you may look for options in magisk or even Xda for possibilities.
First of all, let me say that I should have read closely the first page, because in there says that this ROM uses the google apps.
Thank you arnabj for answering me.
The main reason that I choose the Xiaomi EU in first place, is because that ROM come with Xiaomi apps for dialer, contacts and messaging. Unfortunetly I think that they aren't working on RN8T ROM, because, not Android 10 and not even MIUI12 is avaiable for the phone.
I know I can use a third party app, but it is not what I wanted...