This is one of the "advanced splash screen scenarios" that the Maui Splash Screen doesn't cover, so you'll need to use per-platform techniques to achieve it.
From Add a splash screen to a .NET MAUI app project:
For more advanced splash screen scenarios, per-platform approaches apply.
There is an open proposal to expand the cross-platform functionality to cover more advanced scenarios at Support background image on splashscreen iOS #12639 and a doc item to explain in more detail how to achieve this at: Custom splash screens for per-platform scenarios #1222
Please be aware that including a branding logo at the bottom is recommended against by both the Android and Apple design guidelines, though you can technically do so on both platforms. I don't know if Google or Apple enforce this in their stores.
On Android see [Set a theme for the splash screen to change its appearance](https://developer.android.com/develop/ui/views/launch/splash-screen#set-theme
You can use
windowSplashScreenBrandingImage
to set an image to be shown at the bottom of the splash screen. However, the design guidelines recommend against using a branding image. <item name="android:windowSplashScreenBrandingImage">@drawable/...</item>
On iOS you can include it in your storyboard. See Specifying your app’s launch screen in the Apple docs and Add a splash screen to a .NET MAUI app project on per-platform approaches #12917 in the Maui repo.
Apple also recommends against logos on the launch screen: Apple Design Patterns - Launching
Don’t advertise. The launch screen isn’t a branding opportunity. Avoid creating a screen that looks like a splash screen or an “About” window, and don’t include logos or other branding elements unless they’re a fixed part of your app’s first screen. If your game or other immersive app displays a solid color before transitioning to the first screen, create a launch screen that displays only that solid color.