Debloating and FOSSing the phone
This is my own guide on how to get privacy on the phone without root need and custom roms.
0. If it's your new phone right now and you're reading this: Go through the first configuration, disable all available options, for example like location services and personalized ads. Skip the google account prompt and set the PIN or password, don't use pattern, because it's too easy to guess it after the fingerprint slides on the screen.
1. Uninstall available bloatware automatically installed on your phone, like facebook, netflix, spotify etc. Then go to the browser and install F-droid store client. Proceed to install and accept the risk that phone can show about installing third party softwares. Go to the F-droid and install AnySoftKeyboard and replace Gboard with this keyboard.
2. Go to the settings, click about phone, and click a few times on the build number or miui version to activate developer options and enable USB debugging. Connect your phone to the available computer and install Android Debug Bridge tools that are available on Windows SDK tools or on Linux adb or android-tools package from your operating system package manager. After installation of the adb tools, install Universal Android Debloater and select whole recommended list (uncheck stuff you want to be on it if you want.) and click uninstall all. You are able to fully degoogle your phone and dexiaoomi it by going to the other tabs that aren't this one called unsafe and search for google services and google frame work and xiaomi framework and uninstall them with any other unwanted google apps that won't work without google services anyway and reboot the phone.
3. Install the most important tools on your phone from F-droid, like Fossify tools, K-9 mail client, Fennec or Mull browser, etc.
4. Install shelter from F-droid to create a work profile for the software that wouldn't work on main phone's (0 user) or need google services to launch at all (the work profile is different and has available play services on it unless you debloat it with UAD, on the user 999), so software that need that can be used on the work profile).