I join other people that have the same problem with Android 12 but I can't find a solution.
I have a MAUI project. When I deploy the project on an emulator the splashscreen is visible as you can see in the following screenshot.
When I test the application on a real device with Android 12, the splashscreen is not visible at all.
I read different posts:
but it is still not working at all. All the posts I found were quite old, at least 1 year, and no one has a solution.
Workaround (not working)
Add a file into your .NET MAUI app with this exact name:
Platforms\Android\Resources\drawable\maui_splash.xml
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" android:opacity="opaque">
<item android:drawable="@color/maui_splash_color" />
<item
android:width="108dp"
android:height="108dp"
android:gravity="center">
<bitmap
android:gravity="fill"
android:src="@drawable/name_of_your_splash_image"
android:mipMap="true"/>
</item>
</layer-list>
Make sure to use the name of your splash screen image in the place of name_of_your_splash_image.
Do you know how to fix it?

There are some known issues about this.
And you can follow them up here: AppIcons and Splash Screens Do Not Render Correctly on Physical Devices.
You can also check this issue :[android] fix MauiSplashScreen on Android 12+.